Reference

Glossary

Watch terminology can be intimidating. Here's everything you need to know, in plain English.

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Automatic Watch: An automatic watch is a mechanical watch that winds itself from the movement of your wrist. A rotor inside swings as you move and tightens the mainspring, so it needs no battery. Worn every day it keeps running; left off for a few days it stops and has to be rewound.
Chronometer (COSC): A chronometer is a watch whose movement has been tested and certified for accuracy by an independent body. In Switzerland that body is COSC, and the movement must keep to about minus four to plus six seconds a day. It is an accuracy grade, not the same thing as a chronograph.
Complication: A complication is the umbrella term for any watch function beyond plain hours, minutes and seconds. A date, chronograph, GMT, moonphase or power reserve are the common examples. Each one adds usefulness, but also makes the calibre more complex and raises the price.
Crystal: A watch crystal is the transparent cover that protects the dial. Three materials are common: sapphire crystal, the hardest and most scratch resistant though costly; mineral glass, cheaper and more prone to scratches but better at resisting shattering; and acrylic, soft and scratch prone yet able to be polished out. An anti-reflective coating cuts glare.
Dial: The dial is the face of the watch: the surface that carries the markers, hands and printed text. It is the backdrop the hands sweep across, and it shapes both legibility and character. Dials come in finishes such as lacquer, sunburst and enamel.
Digital Watch: A digital watch shows the time as numerals on an LCD screen rather than with hands. It is quartz powered and usually adds a stopwatch, alarm, backlight and sometimes world time. Digitals are extremely accurate, inexpensive and tough, and the Casio F-91W and G-Shock are icons of the type.
Dive Watch (Diver): A dive watch has at least 100 metres of water resistance (200 is common for extra margin), a screw-down crown, a unidirectional rotating bezel and strong lume. Professional-grade models meet the ISO 6425 standard, which sets a 100 m minimum, and carry the marking DIVER'S WATCH followed by the rated depth on the dial.
Dress Watch: A dress watch is a thin, minimalist watch made for formal or business wear. It has a small to moderate case, a slim profile that slips under a shirt cuff, a clean dial and usually a leather strap with modest water resistance. It is the opposite of a chunky diver.
Indices: Indices are the hour markers on a dial: the points you read the hands against to tell the time. They can be printed directly onto the dial or applied as separate pieces that sit slightly proud. Common styles are baton, Arabic numerals and Roman numerals, and each affects legibility.
ISO 6425: ISO 6425 is the international standard a watch must meet to be marked a diver's watch. It tests water resistance of at least 100 metres, a timing bezel, legibility in the dark, and resistance to magnetism, shock and salt water. Many Seiko Prospex diver references are built to meet it.
Mechanical Watch: A mechanical watch runs on a wound mainspring and a gear train, with no battery. There are two kinds: automatic, which winds itself through a rotor, and manual, which you wind by hand. It is prized for its craftsmanship and a smooth sweeping seconds hand, keeps time slightly less accurately than quartz, and needs periodic servicing.
Moonphase: A moonphase is a complication that displays the current phase of the moon, from a thin crescent to a full disc, through a small aperture on the dial. It is largely decorative and traditional rather than practical, driven by a moon disc with 59 teeth that a finger on the hour wheel advances one step each day. A standard version drifts about a day every two and a half years, whereas a high-precision version stays within a day for more than a century.
Reference Number: A reference number is the manufacturer code that identifies an exact watch variant. It pins down the combination of case, dial, strap and movement. You use it to look up specifications, source the correct spare parts and check that a watch is authentic. It is usually engraved on the caseback.
Shock Resistance: Shock resistance is a watch's ability to withstand drops and knocks without losing accuracy or breaking, often tested to the ISO 1413 standard. In a mechanical watch, sprung jewel settings such as Incabloc cushion the balance staff pivots so a hard knock does not snap them. A digital quartz watch takes a different route: the Casio G-Shock has no balance wheel to protect, so it floats its electronic module inside a cushioned case instead.
Sports Watch: A sports watch is a durable everyday watch built for activity: higher water resistance, a legible dial, a robust case and bracelet, often rated to 100 metres or more. It is broader than a dedicated diver and sits at the opposite end of the spectrum from a dress watch.
Stainless Steel: Stainless steel is the standard metal for watch cases, usually the surgical-grade 316L alloy. It is corrosion resistant and strong, and it takes both a brushed and a polished finish. It is heavier than titanium and is the default for Orient, Seiko and Citizen cases.
Tourbillon: A tourbillon is a watch complication that mounts the entire escapement inside a rotating cage. Because the cage turns continuously, it averages out the effect of gravity on the watch's rate. It was devised for pocket watches and today is prized mainly as a showcase of hand-finishing and prestige.
Water Resistance: The water resistance figure on a dial is a laboratory pressure rating, not a real diving depth. 30 metres covers hand washing and rain, 50 metres covers showering and shallow swimming, and 100 metres is the ISO 6425 floor for a certified dive watch. No watch is truly waterproof; it is only water resistant.

Water and Diving

8 terms

Terms that explain how watches resist water and what a dive watch actually needs.

ATM and Bar: ATM and bar are the pressure units used for water resistance. One ATM equals about one bar, roughly the static pressure of 10 metres of water, so a 20 ATM watch is rated to 200m. That figure is a laboratory pressure rating, not an actual diving depth.
Depth Rating: Depth rating is the water resistance figure printed on a watch case, given in metres or ATM. It reflects a static pressure test carried out in a lab, not the depth to which you can safely dive in real water.
Dive Watch (Diver): A dive watch has at least 100 metres of water resistance (200 is common for extra margin), a screw-down crown, a unidirectional rotating bezel and strong lume. Professional-grade models meet the ISO 6425 standard, which sets a 100 m minimum, and carry the marking DIVER'S WATCH followed by the rated depth on the dial.
Diver's Extension: A diver extension is a folding or sliding section built into a dive watch clasp. It lets the bracelet open up by a set amount so the watch fits over a thick wetsuit sleeve, then closes back to its normal length on dry land.
Helium Escape Valve: A helium escape valve is a small valve that lets helium atoms vent out of the case during decompression after a saturation dive. As ambient pressure drops, trapped helium would otherwise push against the crystal, so the valve releases it. It only matters to professional saturation divers and is unnecessary on most watches.
ISO 6425: ISO 6425 is the international standard a watch must meet to be marked a diver's watch. It tests water resistance of at least 100 metres, a timing bezel, legibility in the dark, and resistance to magnetism, shock and salt water. Many Seiko Prospex diver references are built to meet it.
Unidirectional Bezel: A unidirectional bezel is a diving bezel that turns one way only, conventionally anticlockwise. You align its zero marker to the minute hand to time the dive. Because it rotates in just one direction, an accidental knock can only make the elapsed time read longer, never shorter, so the diver believes less time remains and surfaces sooner. ISO 6425 requires the timing bezel to resist accidental movement, which in practice means unidirectional rotation.
Water Resistance: The water resistance figure on a dial is a laboratory pressure rating, not a real diving depth. 30 metres covers hand washing and rain, 50 metres covers showering and shallow swimming, and 100 metres is the ISO 6425 floor for a certified dive watch. No watch is truly waterproof; it is only water resistant.

Dial and Hands

11 terms

Everything that makes up the face of a watch and drives legibility: the dial, indices, hands and sub-dials.

Applied Markers: Applied markers are three-dimensional metal hour markers made as separate pieces and pinned onto the dial surface rather than printed on it. Because they stand above the dial, they catch light and cast small shadows, lending the watch a deeper, more premium look than flat printed indices.
California Dial: A California dial mixes Roman numerals across the top half with Arabic numerals on the bottom, usually with a triangle at twelve o'clock. The split numbering is a vintage layout, often associated with World War II era dials, that lends a watch a distinctive retro character; the two numeral families are sometimes said to help the eye fix the hour at a glance.
Chapter Ring: The chapter ring is the band around the edge of the dial that carries the minute or second track. It often sits slightly raised or in a contrasting colour so the scale stands out and the watch reads more cleanly at a glance.
Dial: The dial is the face of the watch: the surface that carries the markers, hands and printed text. It is the backdrop the hands sweep across, and it shapes both legibility and character. Dials come in finishes such as lacquer, sunburst and enamel.
Fumé Dial: A fumé dial, also called a smoked dial, is a dial with a colour gradient that stays bright at the centre and darkens towards the edges. The lighter middle and deep rim give it visible depth, so the surface reads with more dimension than a flat painted dial and shifts with the light.
Hand Styles: Hand styles are the shapes given to a watch's hour and minute hands. Dauphine, sword, baton, Mercedes and snowflake are the most common. The shape you choose sets both legibility and character: slim, faceted hands read as dressy, while broad, lume-filled hands read clearly at a glance.
Indices: Indices are the hour markers on a dial: the points you read the hands against to tell the time. They can be printed directly onto the dial or applied as separate pieces that sit slightly proud. Common styles are baton, Arabic numerals and Roman numerals, and each affects legibility.
Regulator Dial: A regulator dial is a layout that separates the hours, minutes and seconds onto their own axes instead of stacking all three on one central pivot. The design comes from precision reference clocks. Its large, usually central minute hand is built to be read clearly at a glance.
Sandwich Dial: A sandwich dial is a two-layer dial: the top plate is cut out where the numerals and markers sit, and a lower disc filled with luminous material shows through those openings. The result is recessed markers with genuine depth that glow brightly at night.
Sub-dial: A sub-dial is a small auxiliary dial set into the main dial of a watch. It is used for chronograph counters, a running seconds display, a pointer day or date, or a second time zone. By keeping that information separate, it adds function without cluttering the main time readout.
Sunburst Dial: A sunburst dial is a dial surface brushed radially outward from the centre. Those fine lines fan light across the face, so the surface shifts between bright and dark as the watch moves and the colour changes with the viewing angle.

Movement

23 terms

The mechanisms that power a watch: automatic, quartz, Eco-Drive and related concepts.

Amplitude: Amplitude is how far the balance wheel rotates from its rest position to the peak of its swing in a mechanical watch, measured in degrees and read on a timing machine. A healthy figure shows the movement is receiving good energy, while low amplitude points to a tired mainspring, gummed-up oil, or a service that is due.
Automatic Watch: An automatic watch is a mechanical watch that winds itself from the movement of your wrist. A rotor inside swings as you move and tightens the mainspring, so it needs no battery. Worn every day it keeps running; left off for a few days it stops and has to be rewound.
Beat Error: Beat error is the small timing difference between the two swing directions of the balance wheel, measured in milliseconds on a timing machine. A low figure means an even rate, while a high one can be reduced during regulation by resetting the balance's rest position.
Bridge: A bridge is a metal bar screwed over the mainplate that holds the upper pivots of the going-train wheels and balance in place. Fixed at both ends rather than one, it suspends each pivot between two anchor points. Bridges largely define the visible architecture and character of a mechanical calibre.
Calibre: A calibre is the specific movement model inside a watch, usually named by a number such as the Seiko 4R36 or Orient F6922. The calibre tells you the movement type, whether automatic or quartz, and its features such as hacking, hand-winding, beat rate and power reserve.
Eco-Drive: Eco-Drive is Citizen's light-powered quartz technology. A cell behind the dial converts any light into energy, so the watch never needs a battery change and, fully charged, keeps running for months in the dark.
Escape Wheel: The escape wheel is the toothed wheel at the end of the gear train. The pallet fork locks and releases it beat by beat, turning the mainspring's continuous power into the regulated steps that drive the hands. It is the gateway to timekeeping in a mechanical watch.
Gear Train: The gear train is the series of meshed wheels that carries energy from the mainspring barrel to the escapement. Along the way it steps the power down and the speed up, so the hour, minute and seconds hands turn at the correct rate. Because it keeps the watch going, it is also called the going train.
Hacking (Second Stop): Hacking is the feature whereby the seconds hand stops the moment you pull the crown out, letting you set the watch to another timepiece right down to the second. Not every mechanical movement offers it.
Horology: Horology is the science of measuring time and the art of making timepieces. It covers everything that keeps time, from sundials and water clocks to mechanical and quartz watches, including their design, history, and the principles that make them work.
Kinetic: Kinetic is a hybrid system developed by Seiko: the motion of your wrist turns an internal rotor, the energy it generates is stored in a rechargeable cell that Seiko calls a capacitor, and that charge drives a quartz movement. It pairs the self-winding feel of an automatic with quartz accuracy and needs no routine battery change.
Magic Lever: The Magic Lever is Seiko's automatic winding system. An eccentric on the rotor's pivot rocks a small two-pawl lever back and forth; as one claw pulls, the other pushes, so the mainspring winds whichever way the rotor turns. It uses very few parts, making it robust and cheap to manufacture.
Mainplate: The mainplate is the base plate of a movement. Every other part, including the wheels, bridges, winding mechanism and pallet, is mounted onto it. Its holes and seats locate each part in exactly the right place. Its diameter usually defines the calibre's diameter, since it is the foundation everything else sits on.
Mainspring: The mainspring is the coiled steel ribbon that stores a mechanical watch's energy. Winding tensions it, and as it unwinds it slowly releases that energy to the movement. The total energy the spring holds sets how long the watch runs unworn, known as its power reserve.
Mainspring Barrel: The mainspring barrel is the toothed drum that houses the coiled mainspring. As the spring unwinds, the barrel feeds its stored energy into the centre wheel of the going train. Barrel diameter, mainspring length and thickness, and the calibre's energy consumption together set the power reserve.
Manual-Winding (Hand-Wound): A manual-winding (hand-wound) watch is a mechanical watch you power by turning the crown with your fingers rather than from wrist motion. Each turn tightens the mainspring to store energy, so unlike an automatic it must be wound by hand on a regular basis.
Mechanical Watch: A mechanical watch runs on a wound mainspring and a gear train, with no battery. There are two kinds: automatic, which winds itself through a rotor, and manual, which you wind by hand. It is prized for its craftsmanship and a smooth sweeping seconds hand, keeps time slightly less accurately than quartz, and needs periodic servicing.
Pallet Fork: The pallet fork is a small anchor-shaped lever in the escapement. Its two jewelled pallets lock and release the escape wheel in turn, and in doing so it hands a measured push of energy to the balance wheel. That locking and releasing action is what makes a watch tick.
Power Reserve: Power reserve is how long a fully wound mechanical watch keeps running off the wrist. On most automatics it is around 40 hours; some movements reach 70 hours and more.
Quartz Watch: A quartz watch tells the time using a quartz crystal that a battery makes vibrate. It is far more accurate than a mechanical watch and needs next to no maintenance, drifting only about fifteen seconds a month and running for years on a battery, or on light.
Rotor: A rotor is the half-moon weight inside an automatic watch. It swings with the motion of your wrist, and that swing winds the mainspring. You can usually see it turning through a display caseback. Its free swing is what makes an automatic watch self-winding.
Shock Protection System: A shock protection system is a sprung jewel setting that lets the fine pivot of the balance shift slightly on impact and then return to place, so the delicate balance staff does not snap when the watch is dropped. The best known systems are Incabloc, Seiko Diashock and Citizen Parashock.
Solar Movement: A solar movement is a watch powered by light. A cell under the dial converts sunlight or room light into electricity and stores it in a rechargeable cell, so there is no routine battery change. Fully charged, it carries on running for months in the dark.

Materials

7 terms

The materials used in a watch crystal, case and strap: sapphire, mineral, steel, titanium and more.

Acrylic Crystal: Acrylic crystal is a lightweight plastic watch crystal, also called hesalite, that protects the dial. It scratches easily, but those scratches polish straight out, and rather than shattering on impact it tends to flex. It is common on vintage and budget watches.
Hardlex: Hardlex is Seiko's branded hardened mineral crystal. It is tougher and more shatter resistant than ordinary mineral glass, yet softer than sapphire, so keys or grit can still scratch it. You will find it on the Seiko 5 and entry-level Prospex models.
Mineral Crystal: Mineral crystal is a hardened glass fitted over the watch dial. It is far cheaper than sapphire and more resistant to shattering on impact, yet it scratches more readily, rating around 5.5 (roughly 5 to 6) on the Mohs hardness scale against sapphire's 9. Seiko's Hardlex is a branded mineral glass.
Resin: Resin is a tough, lightweight plastic used for watch cases and straps, mostly on affordable and sports watches. It absorbs knocks rather than denting, shrugs off water and sweat, and costs little to make, which is why it defines the classic Casio look.
Sapphire Crystal: Sapphire crystal is the transparent cover over the dial made from synthetic sapphire. It rates a 9 on the Mohs hardness scale, second only to diamond, so it resists scratches far better than mineral glass, although it costs more to produce.
Stainless Steel: Stainless steel is the standard metal for watch cases, usually the surgical-grade 316L alloy. It is corrosion resistant and strong, and it takes both a brushed and a polished finish. It is heavier than titanium and is the default for Orient, Seiko and Citizen cases.
Titanium: Titanium is a case metal much lighter than steel and hypoallergenic, with high strength. It resists corrosion well, but it scratches more readily than steel unless its surface has been hardened. Citizen uses titanium across many of its watches, which is why you meet it so often.

Complications

20 terms

The extra functions a watch performs beyond telling the time: chronograph, GMT, date and more.

Alarm Watch: An alarm watch is a watch that sounds an audible alert at a time you set ahead. In mechanical alarm calibres a small hammer strikes the case or a gong, whereas digital watches use a tiny buzzer. You set the alarm time and switch it on or off with a second crown or a button.
Big Date: A big date is a date display that shows the date in larger digits than a standard small date. It usually uses two side-by-side discs in a single aperture or a twin aperture, so the date reads at a glance, without squinting. The clearer look requires extra mechanism inside the calibre.
Caller vs True GMT: Caller and true GMT are the two ways a GMT watch can work. On a true or flyer GMT, the local hour hand jumps independently as you travel, which is ideal for trips. On a caller or office GMT, only the 24-hour hand moves, which suits tracking a second zone from your desk.
Chronograph: A chronograph is a stopwatch complication that times an elapsed interval without disturbing normal timekeeping. Side pushers start, stop and reset the counter, with the seconds usually supported by minute and hour sub-dials. It comes in both quartz and mechanical versions.
Complication: A complication is the umbrella term for any watch function beyond plain hours, minutes and seconds. A date, chronograph, GMT, moonphase or power reserve are the common examples. Each one adds usefulness, but also makes the calibre more complex and raises the price.
Date Window: A date window is a simple complication that shows the day of the month through a small aperture on the dial. It is generally considered the most common complication of all. Window variants include the day-date and the big date, while a pointer date is the windowless alternative that marks the date with its own hand. Most need manual correction after short months, and many offer a quickset through the crown.
Day-Date: Day-Date is a complication that displays both the weekday and the date of the month on the dial. The day appears either in a wide arc near 12 or in a window beside the date, depending on the design. Both indications can usually be quickset independently, which makes resetting the watch after short months quick.
Equation of Time: The equation of time is a rare complication that displays the difference between the mean clock time your watch keeps and true solar time, set by the sun's actual position in the sky. This gap shifts across the year, reaching roughly plus or minus 16 minutes. It is a haute horlogerie showpiece.
Flyback Chronograph: A flyback chronograph is a complication that resets and instantly restarts a running chronograph with a single press, rather than the usual stop, reset, start sequence. Developed for pilots and navigators, it is a higher-end feature rarely found on affordable quartz chronographs.
GMT: A GMT is a complication that displays a second time zone with an extra 24-hour hand, normally read against a 24-hour bezel or track. It lets you follow home and local time at once, which is why travellers favour it. The affordable Seiko 5 GMT is one such example, a caller GMT suited to tracking a second zone from a fixed base.
Jumping Hour: A jumping hour is a display that shows the hour as a single number in a window, snapping instantly to the next digit at the top of each hour, while the minutes are read conventionally. Because a disc jumps rather than a hand sweeping a scale, it is a distinctive way to read the time.
Monopusher Chronograph: A monopusher chronograph runs its start, stop and reset functions through a single button that cycles through them in turn. On many monopushers this button is built into the crown, coaxial with it, giving the watch a tidy case profile, while others place it on the case at the 2 o'clock position. It harks back to the early days of the chronograph and lets you time only one continuous event at a time.
Moonphase: A moonphase is a complication that displays the current phase of the moon, from a thin crescent to a full disc, through a small aperture on the dial. It is largely decorative and traditional rather than practical, driven by a moon disc with 59 teeth that a finger on the hour wheel advances one step each day. A standard version drifts about a day every two and a half years, whereas a high-precision version stays within a day for more than a century.
Pulsometer: A pulsometer is a chronograph scale calibrated to read heart rate directly. You start the chronograph, count a set number of heartbeats, then stop it, and the chronograph's seconds hand points to beats per minute on the scale. The complication has its origins in doctors' watches.
Retrograde: A retrograde is a display where a hand travels along an arc rather than a full circle, then jumps instantly back to the start once it reaches the end of the scale. It is most often used for the date, day or seconds, and its movement lends the dial a distinctive sense of life.
Split-Seconds Chronograph: A split-seconds chronograph, also known as a rattrapante, is a chronograph with two stacked second hands. It lets you time two events that start together but finish apart, such as two lap times. Because the mechanism is complex to build, it appears almost only in high-end watches.
Tachymeter: A tachymeter is a fixed scale around the bezel or dial rim that converts elapsed seconds into speed. You start the chronograph at a marker, stop it after a known distance, and the seconds hand points to the average speed. It needs a chronograph to be used.
Telemeter: A telemeter is a fixed scale printed on a chronograph dial or its rim that reads the distance to an event you can both see and hear by timing the delay of the sound. You start the chronograph at the flash, stop at the sound, and the seconds hand shows the distance.
Tourbillon: A tourbillon is a watch complication that mounts the entire escapement inside a rotating cage. Because the cage turns continuously, it averages out the effect of gravity on the watch's rate. It was devised for pocket watches and today is prized mainly as a showcase of hand-finishing and prestige.
World Timer: A world timer is a complication that displays the major time zones around the globe at once, using a rotating 24-hour ring read against a fixed ring of cities on the dial. It usually lists 24 reference cities, one per major zone, so a glance gives you the time in each.

Parts

8 terms

The visible components of a watch such as the bezel, the lume and the dial.

Bezel: The bezel is the ring around the crystal at the top of the case, framing the dial. It may be fixed, or it may rotate to measure dive time (a unidirectional diver's bezel), a second time zone (GMT) or speed (tachymeter).
Case: The case is the body of the watch that holds the movement, dial and crystal together. It largely defines the watch's diameter, thickness, water resistance and overall character. Cases come in shapes such as round, tonneau, cushion and square, and in materials like steel, titanium or gold.
Caseback: The caseback is the back cover of a watch case. It seals the movement inside and forms the surface that rests against your wrist. It can be solid or a display (exhibition) caseback, and it either screws down or snaps on. Its engravings usually list model, water resistance, and serial details.
Crown: The crown is the grooved knob on the side of the case. You use it to set the time and date and to wind a mechanical watch. Pushed in it runs and winds a mechanical calibre, pulled out it sets the time and date. A screw-down crown threads shut against a gasket for water resistance.
Crystal: A watch crystal is the transparent cover that protects the dial. Three materials are common: sapphire crystal, the hardest and most scratch resistant though costly; mineral glass, cheaper and more prone to scratches but better at resisting shattering; and acrylic, soft and scratch prone yet able to be polished out. An anti-reflective coating cuts glare.
Lugs: Lugs are the four arms that extend from the case and hold the strap or bracelet. The gap between them sets the lug width, and how far they reach sets the lug-to-lug length. Together they shape how a watch sits on your wrist more than the case diameter alone.
Lume: Lume is the glowing material applied to the hands and markers; it charges in light and glows in the dark, letting you read the watch at night. The most common types are Super-LumiNova and Seiko's LumiBrite.
Screw-down Crown: A screw-down crown threads down onto a gasket to seal the case for water resistance. You unscrew it to set the time, then screw it shut again before any water. It is standard on dive watches, and forgetting to screw it down lets water into the case.

Straps and Bracelets

7 terms

Everything that fastens a watch to the wrist: NATO and leather straps, metal bracelets, lug width and spring bars.

Bracelet: A bracelet is a watch band made of interlocking metal links that fasten to the case. It is usually stainless steel and closes with a clasp at the wrist. Unlike a one-piece leather or fabric strap, you size it by removing or adding individual links.
Jubilee Bracelet: A Jubilee bracelet is a five-link metal watch bracelet known for its smaller polished centre links set between larger brushed outer links. It is more flexible, more refined and dressier than an Oyster bracelet, so it drapes comfortably on the wrist and suits both daily wear and smarter occasions.
Leather Strap: A leather strap is a classic, dressy watch band made from genuine animal hide, most often calfskin, fine-grained boxcalf, or printed alligator-grain leather. It softens, takes the shape of your wrist, and develops a patina with wear over time, but it remains sensitive to water, perspiration and prolonged humidity.
NATO Strap: A NATO strap is a one-piece woven nylon watch strap that threads under the case. It has a military origin, is very secure and is washable. Even if one spring bar fails, the watch stays on your wrist. You size it by the case lug width.
Oyster Bracelet: An Oyster bracelet is a sporty three-link metal watch bracelet made from broad, flat links. It is known for its durability and everyday comfort. Rolex introduced and popularised the design, patenting its version in 1947 and building on earlier flat-link bracelets rather than inventing the metal bracelet outright. Today it is one of the most common bracelet styles on dive and sports watches, and many brands produce their own variants.
Rubber Strap: A rubber strap is a water-resistant watch strap made from rubber or silicone. It is the natural choice for sport and dive watches because it shrugs off sweat and water, wipes clean in seconds, and sits comfortably against the skin. It is also lighter than a steel bracelet. Whether you can swim or dive in it depends on the watch's own water resistance, not the strap.
Spring Bar: A spring bar is the small metal pin with an internal spring that holds a strap or bracelet between the watch lugs. Its sprung tips compress and seat into the lug holes, and a simple spring-bar tool lets you press them in to change a strap at home.

Size and Fit

5 terms

Measurements that decide how a watch sits on the wrist, plus endurance figures like power reserve.

Case Diameter: Case diameter is the width of the watch case across the dial, measured in millimetres and excluding the crown. Common sizes run roughly 36 to 42mm. It is the headline size figure quoted for a watch, but lug-to-lug length does more to decide how the watch actually sits on your wrist.
Case Thickness: Case thickness is how tall the watch stands off your wrist, measured in millimetres. Genuinely slim watches come in around 10mm or under and slip under a cuff, while most modern divers run thick, roughly 12mm and up. Thickness shapes comfort and how a watch sits as much as diameter does.
Lug-to-Lug: Lug-to-lug is the vertical distance from the tip of the upper lug to the tip of the lower lug. It is this measurement, not the case diameter, that decides whether a watch will truly fit your wrist.
Lug Width: Lug width is the gap between the lugs, in millimetres, where the strap fits. It is usually an even number such as 18, 20 or 22mm, and it tells you which straps will fit your watch. Knowing the right figure makes buying a replacement strap easy. It is not the same as lug-to-lug, which is the overall case length.
Wrist Size: Wrist size is the circumference of your wrist, taken with a flexible tape at the narrowest point just behind the wrist bone, usually in millimetres. That figure helps you choose a case diameter, thickness and, above all, lug-to-lug span so a watch sits flat rather than overhanging.

Styles

7 terms

The families that group watches by design and purpose: dive, dress, field, pilot and more.

Digital Watch: A digital watch shows the time as numerals on an LCD screen rather than with hands. It is quartz powered and usually adds a stopwatch, alarm, backlight and sometimes world time. Digitals are extremely accurate, inexpensive and tough, and the Casio F-91W and G-Shock are icons of the type.
Dress Watch: A dress watch is a thin, minimalist watch made for formal or business wear. It has a small to moderate case, a slim profile that slips under a shirt cuff, a clean dial and usually a leather strap with modest water resistance. It is the opposite of a chunky diver.
Field Watch: A field watch is a rugged, highly legible watch derived from military issue. It has a clean, high-contrast dial, often an inner 24-hour track, a modest case usually around 38 to 40mm and a tough build. It typically comes on a NATO or leather strap and is made for everyday utility.
GADA Watch: A GADA watch, short for Go Anywhere Do Anything, is a versatile one-watch piece that copes with work, sport and smart-casual wear reasonably well. It is usually a sturdy sports watch or diver around 38 to 40mm, built to cover most of what one watch realistically needs to do.
Pilot Watch: A pilot watch is an aviation-derived style built for cockpit readability. It has a large, clear dial, high-contrast numerals, an oversized crown that can be operated even whilst wearing gloves, and sometimes a GMT hand for a second time zone. The whole point is fast, error-free reading at a glance.
Sports Watch: A sports watch is a durable everyday watch built for activity: higher water resistance, a legible dial, a robust case and bracelet, often rated to 100 metres or more. It is broader than a dedicated diver and sits at the opposite end of the spectrum from a dress watch.
Tool Watch: A tool watch is a watch built to do a job, such as diving, flying or fieldwork. It puts legibility and durability first and pushes decoration into the background. In that sense it is the opposite of a dress watch, designed for hard, practical use rather than for show.

Standards

7 terms

The certifications and tests behind a watch's accuracy, water resistance, magnetism and shock: ISO 6425, COSC and more.

Accuracy (Daily Deviation): Accuracy describes how far a watch drifts from true time, given in seconds per day. A quartz watch drifts around 15 seconds a month, while a good mechanical drifts a few seconds a day. It is a property of the movement type, not a fault.
Antimagnetic: Antimagnetic describes how well a watch resists magnetic fields. Magnetism can make a mechanical watch run fast or stop altogether, and the resistance is rated in gauss or to the ISO 764 standard. A soft-iron inner case or silicon parts add the protection.
Chronometer (COSC): A chronometer is a watch whose movement has been tested and certified for accuracy by an independent body. In Switzerland that body is COSC, and the movement must keep to about minus four to plus six seconds a day. It is an accuracy grade, not the same thing as a chronograph.
Japan Movement: Japan movement is a label meaning a watch's movement was made in Japan, by makers such as Seiko, Citizen or Orient. Japanese calibres are known for being reliable, accurate and affordable. Japan made usually refers to the whole watch, whereas Japan movement points only to the engine inside it.
Reference Number: A reference number is the manufacturer code that identifies an exact watch variant. It pins down the combination of case, dial, strap and movement. You use it to look up specifications, source the correct spare parts and check that a watch is authentic. It is usually engraved on the caseback.
Shock Resistance: Shock resistance is a watch's ability to withstand drops and knocks without losing accuracy or breaking, often tested to the ISO 1413 standard. In a mechanical watch, sprung jewel settings such as Incabloc cushion the balance staff pivots so a hard knock does not snap them. A digital quartz watch takes a different route: the Casio G-Shock has no balance wheel to protect, so it floats its electronic module inside a cushioned case instead.
Swiss Made: Swiss Made is a legally protected label indicating a watch is of Swiss origin. The movement must be Swiss, assembled, inspected and technically developed in Switzerland, the whole watch must be cased and inspected there, and at least sixty per cent of total manufacturing cost must arise in Switzerland. It signals origin, not an automatic quality grade.

Maintenance

6 terms

How to keep a watch healthy for years: servicing, water-resistance testing, storage and winding.

Demagnetising: Demagnetising is the process of clearing the magnetic field from the magnetised parts of a mechanical watch. When a watch suddenly begins running very fast, magnetism is often to blame. A small tool called a demagnetiser puts it right in seconds, cheaply.
Gasket: A gasket is a rubber ring fitted at the crown, caseback and crystal that keeps water and dust out. It compresses as the watch closes, sealing the gaps. Because rubber hardens and loses its spring with age, gaskets need periodic replacement.
Pressure Test: A pressure test confirms a watch's water resistance on a machine before you trust it in water. A dry test uses air pressure to detect case leaks, while a wet test submerges the watch under pressure. It is essential after any battery change or service.
Regulation: Regulation is the fine adjustment that brings a mechanical watch closer to true time. By moving the regulator lever, a watchmaker alters the effective length of the balance spring, which speeds up or slows the oscillation and reduces how many seconds the watch gains or loses each day.
Servicing: A service is a full overhaul where a watchmaker opens the watch, cleans the movement out, replaces worn gaskets and oils, then reseals and tests it. Mechanical watches need a service every few years and quartz manages far less often. It keeps both timekeeping and water resistance reliable.
Watch Winder: A watch winder is a motorised box that gently rotates an automatic watch to keep it wound and running while you are not wearing it. It is handy for a watch with a date, a perpetual calendar that is slow to reset, or a collection in rotation. Hand-wound and quartz watches do not need one, so for most owners it is largely a convenience rather than a requirement.

All terms

Accuracy (Daily Deviation): Accuracy describes how far a watch drifts from true time, given in seconds per day. A quartz watch drifts around 15 seconds a month, while a good mechanical drifts a few seconds a day. It is a property of the movement type, not a fault.
Acrylic Crystal: Acrylic crystal is a lightweight plastic watch crystal, also called hesalite, that protects the dial. It scratches easily, but those scratches polish straight out, and rather than shattering on impact it tends to flex. It is common on vintage and budget watches.
Alarm Watch: An alarm watch is a watch that sounds an audible alert at a time you set ahead. In mechanical alarm calibres a small hammer strikes the case or a gong, whereas digital watches use a tiny buzzer. You set the alarm time and switch it on or off with a second crown or a button.
Amplitude: Amplitude is how far the balance wheel rotates from its rest position to the peak of its swing in a mechanical watch, measured in degrees and read on a timing machine. A healthy figure shows the movement is receiving good energy, while low amplitude points to a tired mainspring, gummed-up oil, or a service that is due.
Antimagnetic: Antimagnetic describes how well a watch resists magnetic fields. Magnetism can make a mechanical watch run fast or stop altogether, and the resistance is rated in gauss or to the ISO 764 standard. A soft-iron inner case or silicon parts add the protection.
Applied Markers: Applied markers are three-dimensional metal hour markers made as separate pieces and pinned onto the dial surface rather than printed on it. Because they stand above the dial, they catch light and cast small shadows, lending the watch a deeper, more premium look than flat printed indices.
ATM and Bar: ATM and bar are the pressure units used for water resistance. One ATM equals about one bar, roughly the static pressure of 10 metres of water, so a 20 ATM watch is rated to 200m. That figure is a laboratory pressure rating, not an actual diving depth.
Automatic Watch: An automatic watch is a mechanical watch that winds itself from the movement of your wrist. A rotor inside swings as you move and tightens the mainspring, so it needs no battery. Worn every day it keeps running; left off for a few days it stops and has to be rewound.
Beat Error: Beat error is the small timing difference between the two swing directions of the balance wheel, measured in milliseconds on a timing machine. A low figure means an even rate, while a high one can be reduced during regulation by resetting the balance's rest position.
Bezel: The bezel is the ring around the crystal at the top of the case, framing the dial. It may be fixed, or it may rotate to measure dive time (a unidirectional diver's bezel), a second time zone (GMT) or speed (tachymeter).
Big Date: A big date is a date display that shows the date in larger digits than a standard small date. It usually uses two side-by-side discs in a single aperture or a twin aperture, so the date reads at a glance, without squinting. The clearer look requires extra mechanism inside the calibre.
Bracelet: A bracelet is a watch band made of interlocking metal links that fasten to the case. It is usually stainless steel and closes with a clasp at the wrist. Unlike a one-piece leather or fabric strap, you size it by removing or adding individual links.
Bridge: A bridge is a metal bar screwed over the mainplate that holds the upper pivots of the going-train wheels and balance in place. Fixed at both ends rather than one, it suspends each pivot between two anchor points. Bridges largely define the visible architecture and character of a mechanical calibre.
Calibre: A calibre is the specific movement model inside a watch, usually named by a number such as the Seiko 4R36 or Orient F6922. The calibre tells you the movement type, whether automatic or quartz, and its features such as hacking, hand-winding, beat rate and power reserve.
California Dial: A California dial mixes Roman numerals across the top half with Arabic numerals on the bottom, usually with a triangle at twelve o'clock. The split numbering is a vintage layout, often associated with World War II era dials, that lends a watch a distinctive retro character; the two numeral families are sometimes said to help the eye fix the hour at a glance.
Caller vs True GMT: Caller and true GMT are the two ways a GMT watch can work. On a true or flyer GMT, the local hour hand jumps independently as you travel, which is ideal for trips. On a caller or office GMT, only the 24-hour hand moves, which suits tracking a second zone from your desk.
Case: The case is the body of the watch that holds the movement, dial and crystal together. It largely defines the watch's diameter, thickness, water resistance and overall character. Cases come in shapes such as round, tonneau, cushion and square, and in materials like steel, titanium or gold.
Case Diameter: Case diameter is the width of the watch case across the dial, measured in millimetres and excluding the crown. Common sizes run roughly 36 to 42mm. It is the headline size figure quoted for a watch, but lug-to-lug length does more to decide how the watch actually sits on your wrist.
Case Thickness: Case thickness is how tall the watch stands off your wrist, measured in millimetres. Genuinely slim watches come in around 10mm or under and slip under a cuff, while most modern divers run thick, roughly 12mm and up. Thickness shapes comfort and how a watch sits as much as diameter does.
Caseback: The caseback is the back cover of a watch case. It seals the movement inside and forms the surface that rests against your wrist. It can be solid or a display (exhibition) caseback, and it either screws down or snaps on. Its engravings usually list model, water resistance, and serial details.
Chapter Ring: The chapter ring is the band around the edge of the dial that carries the minute or second track. It often sits slightly raised or in a contrasting colour so the scale stands out and the watch reads more cleanly at a glance.
Chronograph: A chronograph is a stopwatch complication that times an elapsed interval without disturbing normal timekeeping. Side pushers start, stop and reset the counter, with the seconds usually supported by minute and hour sub-dials. It comes in both quartz and mechanical versions.
Chronometer (COSC): A chronometer is a watch whose movement has been tested and certified for accuracy by an independent body. In Switzerland that body is COSC, and the movement must keep to about minus four to plus six seconds a day. It is an accuracy grade, not the same thing as a chronograph.
Complication: A complication is the umbrella term for any watch function beyond plain hours, minutes and seconds. A date, chronograph, GMT, moonphase or power reserve are the common examples. Each one adds usefulness, but also makes the calibre more complex and raises the price.
Crown: The crown is the grooved knob on the side of the case. You use it to set the time and date and to wind a mechanical watch. Pushed in it runs and winds a mechanical calibre, pulled out it sets the time and date. A screw-down crown threads shut against a gasket for water resistance.
Crystal: A watch crystal is the transparent cover that protects the dial. Three materials are common: sapphire crystal, the hardest and most scratch resistant though costly; mineral glass, cheaper and more prone to scratches but better at resisting shattering; and acrylic, soft and scratch prone yet able to be polished out. An anti-reflective coating cuts glare.
Date Window: A date window is a simple complication that shows the day of the month through a small aperture on the dial. It is generally considered the most common complication of all. Window variants include the day-date and the big date, while a pointer date is the windowless alternative that marks the date with its own hand. Most need manual correction after short months, and many offer a quickset through the crown.
Day-Date: Day-Date is a complication that displays both the weekday and the date of the month on the dial. The day appears either in a wide arc near 12 or in a window beside the date, depending on the design. Both indications can usually be quickset independently, which makes resetting the watch after short months quick.
Demagnetising: Demagnetising is the process of clearing the magnetic field from the magnetised parts of a mechanical watch. When a watch suddenly begins running very fast, magnetism is often to blame. A small tool called a demagnetiser puts it right in seconds, cheaply.
Depth Rating: Depth rating is the water resistance figure printed on a watch case, given in metres or ATM. It reflects a static pressure test carried out in a lab, not the depth to which you can safely dive in real water.
Dial: The dial is the face of the watch: the surface that carries the markers, hands and printed text. It is the backdrop the hands sweep across, and it shapes both legibility and character. Dials come in finishes such as lacquer, sunburst and enamel.
Digital Watch: A digital watch shows the time as numerals on an LCD screen rather than with hands. It is quartz powered and usually adds a stopwatch, alarm, backlight and sometimes world time. Digitals are extremely accurate, inexpensive and tough, and the Casio F-91W and G-Shock are icons of the type.
Dive Watch (Diver): A dive watch has at least 100 metres of water resistance (200 is common for extra margin), a screw-down crown, a unidirectional rotating bezel and strong lume. Professional-grade models meet the ISO 6425 standard, which sets a 100 m minimum, and carry the marking DIVER'S WATCH followed by the rated depth on the dial.
Diver's Extension: A diver extension is a folding or sliding section built into a dive watch clasp. It lets the bracelet open up by a set amount so the watch fits over a thick wetsuit sleeve, then closes back to its normal length on dry land.
Dress Watch: A dress watch is a thin, minimalist watch made for formal or business wear. It has a small to moderate case, a slim profile that slips under a shirt cuff, a clean dial and usually a leather strap with modest water resistance. It is the opposite of a chunky diver.
Eco-Drive: Eco-Drive is Citizen's light-powered quartz technology. A cell behind the dial converts any light into energy, so the watch never needs a battery change and, fully charged, keeps running for months in the dark.
Equation of Time: The equation of time is a rare complication that displays the difference between the mean clock time your watch keeps and true solar time, set by the sun's actual position in the sky. This gap shifts across the year, reaching roughly plus or minus 16 minutes. It is a haute horlogerie showpiece.
Escape Wheel: The escape wheel is the toothed wheel at the end of the gear train. The pallet fork locks and releases it beat by beat, turning the mainspring's continuous power into the regulated steps that drive the hands. It is the gateway to timekeeping in a mechanical watch.
Field Watch: A field watch is a rugged, highly legible watch derived from military issue. It has a clean, high-contrast dial, often an inner 24-hour track, a modest case usually around 38 to 40mm and a tough build. It typically comes on a NATO or leather strap and is made for everyday utility.
Flyback Chronograph: A flyback chronograph is a complication that resets and instantly restarts a running chronograph with a single press, rather than the usual stop, reset, start sequence. Developed for pilots and navigators, it is a higher-end feature rarely found on affordable quartz chronographs.
Fumé Dial: A fumé dial, also called a smoked dial, is a dial with a colour gradient that stays bright at the centre and darkens towards the edges. The lighter middle and deep rim give it visible depth, so the surface reads with more dimension than a flat painted dial and shifts with the light.
GADA Watch: A GADA watch, short for Go Anywhere Do Anything, is a versatile one-watch piece that copes with work, sport and smart-casual wear reasonably well. It is usually a sturdy sports watch or diver around 38 to 40mm, built to cover most of what one watch realistically needs to do.
Gasket: A gasket is a rubber ring fitted at the crown, caseback and crystal that keeps water and dust out. It compresses as the watch closes, sealing the gaps. Because rubber hardens and loses its spring with age, gaskets need periodic replacement.
Gear Train: The gear train is the series of meshed wheels that carries energy from the mainspring barrel to the escapement. Along the way it steps the power down and the speed up, so the hour, minute and seconds hands turn at the correct rate. Because it keeps the watch going, it is also called the going train.
GMT: A GMT is a complication that displays a second time zone with an extra 24-hour hand, normally read against a 24-hour bezel or track. It lets you follow home and local time at once, which is why travellers favour it. The affordable Seiko 5 GMT is one such example, a caller GMT suited to tracking a second zone from a fixed base.
Hacking (Second Stop): Hacking is the feature whereby the seconds hand stops the moment you pull the crown out, letting you set the watch to another timepiece right down to the second. Not every mechanical movement offers it.
Hand Styles: Hand styles are the shapes given to a watch's hour and minute hands. Dauphine, sword, baton, Mercedes and snowflake are the most common. The shape you choose sets both legibility and character: slim, faceted hands read as dressy, while broad, lume-filled hands read clearly at a glance.
Hardlex: Hardlex is Seiko's branded hardened mineral crystal. It is tougher and more shatter resistant than ordinary mineral glass, yet softer than sapphire, so keys or grit can still scratch it. You will find it on the Seiko 5 and entry-level Prospex models.
Helium Escape Valve: A helium escape valve is a small valve that lets helium atoms vent out of the case during decompression after a saturation dive. As ambient pressure drops, trapped helium would otherwise push against the crystal, so the valve releases it. It only matters to professional saturation divers and is unnecessary on most watches.
Horology: Horology is the science of measuring time and the art of making timepieces. It covers everything that keeps time, from sundials and water clocks to mechanical and quartz watches, including their design, history, and the principles that make them work.
Indices: Indices are the hour markers on a dial: the points you read the hands against to tell the time. They can be printed directly onto the dial or applied as separate pieces that sit slightly proud. Common styles are baton, Arabic numerals and Roman numerals, and each affects legibility.
ISO 6425: ISO 6425 is the international standard a watch must meet to be marked a diver's watch. It tests water resistance of at least 100 metres, a timing bezel, legibility in the dark, and resistance to magnetism, shock and salt water. Many Seiko Prospex diver references are built to meet it.
Japan Movement: Japan movement is a label meaning a watch's movement was made in Japan, by makers such as Seiko, Citizen or Orient. Japanese calibres are known for being reliable, accurate and affordable. Japan made usually refers to the whole watch, whereas Japan movement points only to the engine inside it.
Jubilee Bracelet: A Jubilee bracelet is a five-link metal watch bracelet known for its smaller polished centre links set between larger brushed outer links. It is more flexible, more refined and dressier than an Oyster bracelet, so it drapes comfortably on the wrist and suits both daily wear and smarter occasions.
Jumping Hour: A jumping hour is a display that shows the hour as a single number in a window, snapping instantly to the next digit at the top of each hour, while the minutes are read conventionally. Because a disc jumps rather than a hand sweeping a scale, it is a distinctive way to read the time.
Kinetic: Kinetic is a hybrid system developed by Seiko: the motion of your wrist turns an internal rotor, the energy it generates is stored in a rechargeable cell that Seiko calls a capacitor, and that charge drives a quartz movement. It pairs the self-winding feel of an automatic with quartz accuracy and needs no routine battery change.
Leather Strap: A leather strap is a classic, dressy watch band made from genuine animal hide, most often calfskin, fine-grained boxcalf, or printed alligator-grain leather. It softens, takes the shape of your wrist, and develops a patina with wear over time, but it remains sensitive to water, perspiration and prolonged humidity.
Lug-to-Lug: Lug-to-lug is the vertical distance from the tip of the upper lug to the tip of the lower lug. It is this measurement, not the case diameter, that decides whether a watch will truly fit your wrist.
Lug Width: Lug width is the gap between the lugs, in millimetres, where the strap fits. It is usually an even number such as 18, 20 or 22mm, and it tells you which straps will fit your watch. Knowing the right figure makes buying a replacement strap easy. It is not the same as lug-to-lug, which is the overall case length.
Lugs: Lugs are the four arms that extend from the case and hold the strap or bracelet. The gap between them sets the lug width, and how far they reach sets the lug-to-lug length. Together they shape how a watch sits on your wrist more than the case diameter alone.
Lume: Lume is the glowing material applied to the hands and markers; it charges in light and glows in the dark, letting you read the watch at night. The most common types are Super-LumiNova and Seiko's LumiBrite.
Magic Lever: The Magic Lever is Seiko's automatic winding system. An eccentric on the rotor's pivot rocks a small two-pawl lever back and forth; as one claw pulls, the other pushes, so the mainspring winds whichever way the rotor turns. It uses very few parts, making it robust and cheap to manufacture.
Mainplate: The mainplate is the base plate of a movement. Every other part, including the wheels, bridges, winding mechanism and pallet, is mounted onto it. Its holes and seats locate each part in exactly the right place. Its diameter usually defines the calibre's diameter, since it is the foundation everything else sits on.
Mainspring: The mainspring is the coiled steel ribbon that stores a mechanical watch's energy. Winding tensions it, and as it unwinds it slowly releases that energy to the movement. The total energy the spring holds sets how long the watch runs unworn, known as its power reserve.
Mainspring Barrel: The mainspring barrel is the toothed drum that houses the coiled mainspring. As the spring unwinds, the barrel feeds its stored energy into the centre wheel of the going train. Barrel diameter, mainspring length and thickness, and the calibre's energy consumption together set the power reserve.
Manual-Winding (Hand-Wound): A manual-winding (hand-wound) watch is a mechanical watch you power by turning the crown with your fingers rather than from wrist motion. Each turn tightens the mainspring to store energy, so unlike an automatic it must be wound by hand on a regular basis.
Mechanical Watch: A mechanical watch runs on a wound mainspring and a gear train, with no battery. There are two kinds: automatic, which winds itself through a rotor, and manual, which you wind by hand. It is prized for its craftsmanship and a smooth sweeping seconds hand, keeps time slightly less accurately than quartz, and needs periodic servicing.
Mineral Crystal: Mineral crystal is a hardened glass fitted over the watch dial. It is far cheaper than sapphire and more resistant to shattering on impact, yet it scratches more readily, rating around 5.5 (roughly 5 to 6) on the Mohs hardness scale against sapphire's 9. Seiko's Hardlex is a branded mineral glass.
Monopusher Chronograph: A monopusher chronograph runs its start, stop and reset functions through a single button that cycles through them in turn. On many monopushers this button is built into the crown, coaxial with it, giving the watch a tidy case profile, while others place it on the case at the 2 o'clock position. It harks back to the early days of the chronograph and lets you time only one continuous event at a time.
Moonphase: A moonphase is a complication that displays the current phase of the moon, from a thin crescent to a full disc, through a small aperture on the dial. It is largely decorative and traditional rather than practical, driven by a moon disc with 59 teeth that a finger on the hour wheel advances one step each day. A standard version drifts about a day every two and a half years, whereas a high-precision version stays within a day for more than a century.
NATO Strap: A NATO strap is a one-piece woven nylon watch strap that threads under the case. It has a military origin, is very secure and is washable. Even if one spring bar fails, the watch stays on your wrist. You size it by the case lug width.
Oyster Bracelet: An Oyster bracelet is a sporty three-link metal watch bracelet made from broad, flat links. It is known for its durability and everyday comfort. Rolex introduced and popularised the design, patenting its version in 1947 and building on earlier flat-link bracelets rather than inventing the metal bracelet outright. Today it is one of the most common bracelet styles on dive and sports watches, and many brands produce their own variants.
Pallet Fork: The pallet fork is a small anchor-shaped lever in the escapement. Its two jewelled pallets lock and release the escape wheel in turn, and in doing so it hands a measured push of energy to the balance wheel. That locking and releasing action is what makes a watch tick.
Pilot Watch: A pilot watch is an aviation-derived style built for cockpit readability. It has a large, clear dial, high-contrast numerals, an oversized crown that can be operated even whilst wearing gloves, and sometimes a GMT hand for a second time zone. The whole point is fast, error-free reading at a glance.
Power Reserve: Power reserve is how long a fully wound mechanical watch keeps running off the wrist. On most automatics it is around 40 hours; some movements reach 70 hours and more.
Pressure Test: A pressure test confirms a watch's water resistance on a machine before you trust it in water. A dry test uses air pressure to detect case leaks, while a wet test submerges the watch under pressure. It is essential after any battery change or service.
Pulsometer: A pulsometer is a chronograph scale calibrated to read heart rate directly. You start the chronograph, count a set number of heartbeats, then stop it, and the chronograph's seconds hand points to beats per minute on the scale. The complication has its origins in doctors' watches.
Quartz Watch: A quartz watch tells the time using a quartz crystal that a battery makes vibrate. It is far more accurate than a mechanical watch and needs next to no maintenance, drifting only about fifteen seconds a month and running for years on a battery, or on light.
Reference Number: A reference number is the manufacturer code that identifies an exact watch variant. It pins down the combination of case, dial, strap and movement. You use it to look up specifications, source the correct spare parts and check that a watch is authentic. It is usually engraved on the caseback.
Regulation: Regulation is the fine adjustment that brings a mechanical watch closer to true time. By moving the regulator lever, a watchmaker alters the effective length of the balance spring, which speeds up or slows the oscillation and reduces how many seconds the watch gains or loses each day.
Regulator Dial: A regulator dial is a layout that separates the hours, minutes and seconds onto their own axes instead of stacking all three on one central pivot. The design comes from precision reference clocks. Its large, usually central minute hand is built to be read clearly at a glance.
Resin: Resin is a tough, lightweight plastic used for watch cases and straps, mostly on affordable and sports watches. It absorbs knocks rather than denting, shrugs off water and sweat, and costs little to make, which is why it defines the classic Casio look.
Retrograde: A retrograde is a display where a hand travels along an arc rather than a full circle, then jumps instantly back to the start once it reaches the end of the scale. It is most often used for the date, day or seconds, and its movement lends the dial a distinctive sense of life.
Rotor: A rotor is the half-moon weight inside an automatic watch. It swings with the motion of your wrist, and that swing winds the mainspring. You can usually see it turning through a display caseback. Its free swing is what makes an automatic watch self-winding.
Rubber Strap: A rubber strap is a water-resistant watch strap made from rubber or silicone. It is the natural choice for sport and dive watches because it shrugs off sweat and water, wipes clean in seconds, and sits comfortably against the skin. It is also lighter than a steel bracelet. Whether you can swim or dive in it depends on the watch's own water resistance, not the strap.
Sandwich Dial: A sandwich dial is a two-layer dial: the top plate is cut out where the numerals and markers sit, and a lower disc filled with luminous material shows through those openings. The result is recessed markers with genuine depth that glow brightly at night.
Sapphire Crystal: Sapphire crystal is the transparent cover over the dial made from synthetic sapphire. It rates a 9 on the Mohs hardness scale, second only to diamond, so it resists scratches far better than mineral glass, although it costs more to produce.
Screw-down Crown: A screw-down crown threads down onto a gasket to seal the case for water resistance. You unscrew it to set the time, then screw it shut again before any water. It is standard on dive watches, and forgetting to screw it down lets water into the case.
Servicing: A service is a full overhaul where a watchmaker opens the watch, cleans the movement out, replaces worn gaskets and oils, then reseals and tests it. Mechanical watches need a service every few years and quartz manages far less often. It keeps both timekeeping and water resistance reliable.
Shock Protection System: A shock protection system is a sprung jewel setting that lets the fine pivot of the balance shift slightly on impact and then return to place, so the delicate balance staff does not snap when the watch is dropped. The best known systems are Incabloc, Seiko Diashock and Citizen Parashock.
Shock Resistance: Shock resistance is a watch's ability to withstand drops and knocks without losing accuracy or breaking, often tested to the ISO 1413 standard. In a mechanical watch, sprung jewel settings such as Incabloc cushion the balance staff pivots so a hard knock does not snap them. A digital quartz watch takes a different route: the Casio G-Shock has no balance wheel to protect, so it floats its electronic module inside a cushioned case instead.
Solar Movement: A solar movement is a watch powered by light. A cell under the dial converts sunlight or room light into electricity and stores it in a rechargeable cell, so there is no routine battery change. Fully charged, it carries on running for months in the dark.
Split-Seconds Chronograph: A split-seconds chronograph, also known as a rattrapante, is a chronograph with two stacked second hands. It lets you time two events that start together but finish apart, such as two lap times. Because the mechanism is complex to build, it appears almost only in high-end watches.
Sports Watch: A sports watch is a durable everyday watch built for activity: higher water resistance, a legible dial, a robust case and bracelet, often rated to 100 metres or more. It is broader than a dedicated diver and sits at the opposite end of the spectrum from a dress watch.
Spring Bar: A spring bar is the small metal pin with an internal spring that holds a strap or bracelet between the watch lugs. Its sprung tips compress and seat into the lug holes, and a simple spring-bar tool lets you press them in to change a strap at home.
Stainless Steel: Stainless steel is the standard metal for watch cases, usually the surgical-grade 316L alloy. It is corrosion resistant and strong, and it takes both a brushed and a polished finish. It is heavier than titanium and is the default for Orient, Seiko and Citizen cases.
Sub-dial: A sub-dial is a small auxiliary dial set into the main dial of a watch. It is used for chronograph counters, a running seconds display, a pointer day or date, or a second time zone. By keeping that information separate, it adds function without cluttering the main time readout.
Sunburst Dial: A sunburst dial is a dial surface brushed radially outward from the centre. Those fine lines fan light across the face, so the surface shifts between bright and dark as the watch moves and the colour changes with the viewing angle.
Swiss Made: Swiss Made is a legally protected label indicating a watch is of Swiss origin. The movement must be Swiss, assembled, inspected and technically developed in Switzerland, the whole watch must be cased and inspected there, and at least sixty per cent of total manufacturing cost must arise in Switzerland. It signals origin, not an automatic quality grade.
Tachymeter: A tachymeter is a fixed scale around the bezel or dial rim that converts elapsed seconds into speed. You start the chronograph at a marker, stop it after a known distance, and the seconds hand points to the average speed. It needs a chronograph to be used.
Telemeter: A telemeter is a fixed scale printed on a chronograph dial or its rim that reads the distance to an event you can both see and hear by timing the delay of the sound. You start the chronograph at the flash, stop at the sound, and the seconds hand shows the distance.
Titanium: Titanium is a case metal much lighter than steel and hypoallergenic, with high strength. It resists corrosion well, but it scratches more readily than steel unless its surface has been hardened. Citizen uses titanium across many of its watches, which is why you meet it so often.
Tool Watch: A tool watch is a watch built to do a job, such as diving, flying or fieldwork. It puts legibility and durability first and pushes decoration into the background. In that sense it is the opposite of a dress watch, designed for hard, practical use rather than for show.
Tourbillon: A tourbillon is a watch complication that mounts the entire escapement inside a rotating cage. Because the cage turns continuously, it averages out the effect of gravity on the watch's rate. It was devised for pocket watches and today is prized mainly as a showcase of hand-finishing and prestige.
Unidirectional Bezel: A unidirectional bezel is a diving bezel that turns one way only, conventionally anticlockwise. You align its zero marker to the minute hand to time the dive. Because it rotates in just one direction, an accidental knock can only make the elapsed time read longer, never shorter, so the diver believes less time remains and surfaces sooner. ISO 6425 requires the timing bezel to resist accidental movement, which in practice means unidirectional rotation.
Watch Winder: A watch winder is a motorised box that gently rotates an automatic watch to keep it wound and running while you are not wearing it. It is handy for a watch with a date, a perpetual calendar that is slow to reset, or a collection in rotation. Hand-wound and quartz watches do not need one, so for most owners it is largely a convenience rather than a requirement.
Water Resistance: The water resistance figure on a dial is a laboratory pressure rating, not a real diving depth. 30 metres covers hand washing and rain, 50 metres covers showering and shallow swimming, and 100 metres is the ISO 6425 floor for a certified dive watch. No watch is truly waterproof; it is only water resistant.
World Timer: A world timer is a complication that displays the major time zones around the globe at once, using a rotating 24-hour ring read against a fixed ring of cities on the dial. It usually lists 24 reference cities, one per major zone, so a glance gives you the time in each.
Wrist Size: Wrist size is the circumference of your wrist, taken with a flexible tape at the narrowest point just behind the wrist bone, usually in millimetres. That figure helps you choose a case diameter, thickness and, above all, lug-to-lug span so a watch sits flat rather than overhanging.