What Makes an Automatic Watch Work?

Automatic watches feature a mechanical movement, which is a mechanism run by a series of gears and a mainspring to regulate the time. An automatic timepiece needs no winding if worn daily.

Half-Moon Disc

An automatic watch movement is constructed much the same way as the old-style mechanical movements that must be wound daily. The difference is the half-moon disc, or rotor, attached to the movement inside the case that spins with each movement of the wearer's arm. The disc essentially winds the mainspring to keep the watch always running.

No Winding

Daily wearers of automatic watches never need to wind the timepiece, because arm movement continually rotates the disc to power it. If set aside, the watch remains powered up to about 40 hours. If the watch is worn only occasionally, it must be wound. The wearer simply winds the watch like the mechanical version by rotating the crown at the case edge at 3 o'clock.

Can't Break

The mainspring in an automatic watch can't break due to overwinding. The movement features a detent, or pawl, that allows the stem of the crown to slide continuously along the mainspring without stopping.

References

• Time Zone: Mechanical Watch FAQs