VIBRATION:

In watchmaking, a vibration refers to the movement of a Balance or a Pendulum between one of its extreme positions and the other — that is, a half-oscillation, in a single direction. Two successive vibrations, forward then back, make up one complete Oscillation: these two quantities must therefore not be confused, as a movement vibrating at 4 vibrations per second performs only 2 complete oscillations in the same span of time. The Frequency of a Movement mechanical is traditionally expressed in vibrations per hour (vph) or in hertz (number of oscillations per second): a calibre running at 4 Hz thus beats 28,800 vph (4 × 2 × 3600), a calibre at 5 Hz, 36,000 vph. Each vibration corresponds to an impulse transmitted by the escape wheel to the pallets (lever), then from the plate to the balance, and advances the train (wheel train) by a determined step. Increasing the number of vibrations per hour generally improves timekeeping regularity and shock resistance, but increases the energy consumption of the barrel and reduces the power reserve accordingly. The regularity of the vibration, ensured by the isochronism of the balance-hairspring (balance spring) pair, directly determines the accuracy of the timepiece.