\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}.
   (b) 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).

2. (Mach.) A wheel which imparts regularity to the movements
   of any engine or machine; a fly wheel.