Seiko Men Round Purple Watch

The machinery inside a watch that keeps things ticking is called the movement or calibre.

Today the word is a substitute for movement, the complete mechanism with the mainspring, escape wheel, bridges, gear train, and other components, including the rotor in automatic watches. Calibres are either mechanical or quartz-based. While the latter are powered mostly by a battery, the former can either be manual winding, or self-would by an oscillating mass or rotor.