Standards

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

The numbers and marks on a watch often rest on a standard. A chronometer certificate speaks to accuracy, ISO 6425 to dive capability, a gauss figure to magnetic resistance.

The terms in this section explain in plain language what each certification actually measures, so you can tell a real guarantee from a marketing line.

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.