A mainspring is thin blade made of flexible steel that is housed in the barrel wheel. When a mechanical watch is wound, the mainspring coils up to store the energy that is required to power the watch.
The ensemble of fully assembled mechanical components that perform the operations of a watch. Movements are divided into two main categories: mechanical movements that comprise entirely mechanical parts, which can be hand- or automatic-winding, and quartz movements, which are powered by batteries and are regulated electronically by quartz oscillators. (See also: ‘Calibre’.)