Oscillating weight is attached to the automatic system of a watch and is used today to wind a watch by the gestures of the wearer. It first appeared on pocket watches in order to increase the power reserve. It then arrived on wrist watches.

Oscillating weights are made of heavy metals, such as tungsten, gold, or platinum. To keep the center of gravity as far out as possible, sometimes only one outer segment is made of heavy metal.

The first oscillating masses were with stops. This system had the defect that the screws could unscrew when feeling the shocks. A first company patented an automatic system without stops. That’s why this system was only used by one company for two good decades, until the patent became public domain.

When an oscillating mass is free at 360 degrees it can also be called a rotor. There are also micro-rotors, which are attached to the mainplate and not above the bridges, and are smaller. They allow the creation of finer movements.