The spring, energy accumulator

A mechanical watch needs energy to work. This energy is supplied to the mechanism by a spring which is tightened when the watch is wound. This mainspring is housed within a small cylindrical drum known as the barrel.

This spring itself (1) is a long flexible steel strip that is wound by the winding mechanism around the core of the barrel arbor (2) and stores the energy required to run the watch.

Once wound, the spring naturally tries to regain its initial shape by uncoiling, thereby producing the energy required to drive the watch.

The barrel is connected to a toothed wheel (3) meshing with the movement gear-trains.