Vibrations per hour or beats per hour (vph, VPH, bph, BPH) is a mechanical timepiece specification. It is used to express the frequency of a watch movement.
VPH describes the number of times that a vibrating timekeeping component completes half a vibration cycle every hour (counting the balance wheel's back and forth movement separately, as each produces a forward movement in the escape wheel).
In contrast, when measuring the same frequency in Hertz, it describes the number of times that the component completes a whole vibration cycle in a second (counting pairs of forward movement in the escape wheel). The frequency in Hertz can therefore be multiplied by 7,200 (2 ticks ÃÂ 60 seconds ÃÂ 60 minutes) to determine the frequency in VPH.
A higher frequency is a higher timekeeping resolution, and usually indicates a higher precision mechanical movement. This allows a faster recovery from being knocked or bumped, with the tradeoff being a faster accumulation of wear and tear.