Automatic means a watch winds itself from your wrist's natural motion. Inside, a half-moon rotor pivots with the smallest gesture and, through a train of reversing wheels, charges the mainspring. There is no battery, and no need to wind it by hand each day. The first automatic wristwatch came from a British repairer, John Harwood, who developed it in 1923 and patented it in 1924; his weight swept only about 300 degrees and bumped against buffer springs. In 1931 Rolex, working with Aegler, introduced the Perpetual rotor that turned a full 360 degrees without bumpers, and that free-rotating design set the template everyone follows today. Power reserve, the number of hours a watch keeps running off the wrist, is the figure that defines the type.
The real examples run across every budget. At entry level the Seiko 5 Sports, built on Seiko's NH35/4R35 calibre, gives roughly 41 hours of reserve and sits around £240 to £320. A step up, the Hamilton Khaki Field Automatic uses the ETA-based H-10 with an 80-hour reserve and lands near £430 to £590 on a steel bracelet. The Tissot PRX Powermatic 80, again with that 80-hour mainspring, is strong value at about £560. On the luxury side, the Tudor Black Bay 58 runs roughly £3,100 to £4,300, the Omega Seamaster Diver 300M Master Co-Axial is about £5,400, and the Rolex Oyster Perpetual spans £4,500 to £5,200 depending on case size.
When buying, look at a few concrete things. Hacking seconds, where the second hand stops on pulling the crown, lets you set the watch precisely; hand-winding lets you start a stopped watch from the crown. The NH35 offers both, while the older Miyota 8215 skips hacking seconds. Power reserve matters more than spec-sheet bragging: the gap between a 38-hour ETA 2824 and an 80-hour Powermatic 80 is the difference between finding the watch dead or alive on Monday if you took it off Friday night. An automatic suits someone who wears it most days and enjoys the mechanical pulse. Wear it rarely and you will want a watch winder or the habit of winding by hand, the small trade-off for skipping quartz.
Automatic is not the only branch of the winding family. Manual, or hand-wound, watches carry no rotor, allow slimmer cases, but ask for a daily turn of the crown. COSC-certified chronometer calibres promise tighter accuracy at -4/+6 seconds a day, and Omega's Master Chronometer standard adds magnetic resistance on top. Automatic is simply the most practical and most common form of the lot: put it on, move, and it runs.