Hertz (Not the car rental agency 😉)

The frequency of a watch movement can be expressed in Hertz (Hz) or in vibrations per hour (vph), which is also sometimes referred to as A/h. The frequency in Hertz is the number of oscillations per second. Double the hertz figure to get the number of vibrations or semi-oscillations per second. Multiply that number by 3600 (the number of seconds in an hour) to get the vph.