Bal"ance wheel` (?).
1. Horology (a)
A wheel which regulates the beats or pulses of a watch or chronometer, answering to the pendulum of a clock; -- often called simply a balance.
A ratchet-shaped scape wheel, which in some watches is acted upon by the axis of the balance wheel proper (in those watches called a balance).
A wheel which imparts regularity to the movements of any engine or machine; a fly wheel.
© Webster 1913.