Balance Wheel
The oscillating wheel that acts as the time-regulating element in most mechanical watches.
Also known as: balance, balance oscillator
Definition
The balance wheel is the oscillating wheel that forms the mechanical watch's regulator together with the balance spring. After receiving an impulse from the escapement, it rotates one way and then the other as the spring coils and uncoils. The inertia of the balance and elasticity of the spring determine the oscillator's natural period. Each full oscillation contains two vibrations or beats. Modern balances may use adjustable screws, variable-inertia weights or a fixed geometry depending on how the movement is regulated.
Why it matters
The balance wheel is central to mechanical accuracy. Its inertia, poise, shock protection and interaction with the hairspring influence rate stability across positions and conditions.