Using a part called an "escapement." This explains it clearly and succinctly, right at the top: http://en.wikipedia.org/wiki/Mechanical_watch http://en.wikipe

Using a part called an "escapement." This explains it clearly and succinctly, right at the top: http://en.wikipedia.org/wiki/Mechanical_watch http://en.wikipedia.org/wiki/Mechanical_watch EDIT: Seiko created a hybrid watch that I think is really cool. Like a traditional mechanical watch, the sole source of power is a spring, which in turn is wound by the movements of the wearer. However, in place of an escapement, it uses part of the power from the spring to create just enough electric current to excite a quartz crystal, which provides the timing source for the mechanical movements of the watch. Unlike other watches (mechanical or electronic), the second hand doesn't move in steps, but rather rotates smoothly and continuously around the face: http://en.wikipedia.org/wiki/Seiko_spring_drive http://en.wikipedia.org/wiki/Seiko_spring_drive