Base elements → Measurement units

AMPLITUDE

Amplitude expresses the difference between the extreme values of a quantity (of a wave).

In the rate and accuracy measurements of a mechanical watch, amplitude refers to the angle traveled by the balance wheel between the neutral point (equilibrium position) and its extreme position, i.e., the angle covered during a half-vibration. It is measured using a timegrapher (acoustic measurement) or, more rarely, by optical means.

Amplitude measured on a timegrapher

The amplitude of a watch decreases as the energy supplied by the motor organ decreases. To ensure good accuracy, as high an amplitude as possible helps reduce the influence of shocks and gravitational forces. However, the amplitude of a balance wheel–hairspring is limited by its design (typically a maximum of 280°–300°, depending on the lift angle). Beyond these values, a knocking phenomenon occurs, causing the oscillator to overbank and the watch to gain excessively.

Note that a high amplitude reduces the influence of external factors (particularly shocks and accelerations) on the watch’s rate.