Automatic Watch
An automatic watch is a mechanical watch that winds itself from the motion of your wrist. A rotor inside swings as you move and tightens the mainspring, so no battery is needed. Worn regularly it runs nonstop; left off for a few days it stops and needs rewinding.
At the heart of an automatic watch is the rotor, a half-moon weight that spins with the movement of your wrist. As it turns it winds the mainspring, and the stored energy runs the watch. A fully wound watch usually holds around 40 hours of power reserve, so a watch you take off Friday may still be ticking Monday. It is less precise than quartz; a few seconds of drift per day is normal. It needs servicing every few years. The Seiko 5 and Orient Mako are affordable, classic examples of the type.