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 periodically by turning the crown, to provide energy to run the watch. A self-winding watch movement has a mechanism which winds the mainspring. The watch contains an oscillating weight (the rotor), which turns on a pivot. … Continue reading How An Automatic Watch Works