Automatic Watch - How IT Works

How It Works

A mechanical watch is powered by an internal spiral mainspring which turns the gears that move the hands. The spring loses energy as the watch runs, so in a manual watch movement the spring must be wound by turning a small knob on the case, the crown, to provide energy to run the watch. Otherwise, once the watch loses its stored energy, it stops.

A self-winding watch movement has a mechanism which winds the mainspring. The watch contains an eccentric weight (the rotor), which turns on a pivot. The normal movements of the user's arm cause the rotor to pivot on its staff, which is attached to a ratcheted winding mechanism. The motion of the wearer's arm is thereby translated into circular motion of the rotor which, through a series of reverser and reducing gears, eventually winds the mainspring. Modern self-winding mechanisms have two ratchets and wind the mainspring during clockwise and anticlockwise rotor motions.

The fully wound mainspring in a typical watch can store enough energy reserve for roughly two days, allowing the watch to keep running through the night while stationary. In many cases automatic watches can also be wound manually by turning the crown, so the watch can be kept running when not worn, and in case the wearer's wrist motions are not sufficient to keep it wound automatically.