OSCILLATION

Figure 1

The regulating organ (balance, pendulum) performs an oscillation when it has moved from one extreme position (A’) to the other (A”) and then returns to its initial extreme position (A’) (Figure 1). A complete oscillation thus equals two vibrations, the vibration designating the simple travel from one extreme point to the other. This distinction makes it possible to express the frequency of the resonator in two equivalent ways: in oscillations per second, i.e. in hertz (for example 3 Hz), or in vibrations per hour (v/h) — for this same example, 21,600 v/h, since one oscillation per second equals two vibrations multiplied by 3,600 seconds. Physically, the balance-hairspring behaves like a harmonic oscillator: its natural period depends, as a first approximation, only on its inertia and the stiffness (spring rate) of the hairspring, not on the amplitude — a property known as isochronism, essential to the regularity of the rate. The Escapement maintains these oscillations by restoring to them, at each vibration, a fraction of the energy provided by the Barrel, thus compensating for the losses due to friction.