A balance wheel, is the timekeeping component used in the majority of mechanical watches. It is the wheel that oscillates back and forth, being returned toward its centre position by a spiral balance spring. It is driven by the escapement that transfers power from the mainspring via a train of wheels impulsing the balance wheel, inturn permitting the wheels in the train to run down at a specific and constant rate.

It is the movement of the balance wheel being impulsed by the escapement that results in the “Tick-Tock”.