frequency at which the balance wheel and spring oscillate to and fro (back and forth). Frequency, oscillation rate, VPH “Vibrations per hour”, or BPH “beats per hour” are all the same as oscillating frequency. The balance of a mechanical watch generally makes 5 or 6 vibrations per second (18,000-21,600 per hour.) A high-frequency watch makes 8-10 vibrations per second (25,200/28,800/36000/43,200 per hour). Here are the most common mechanical wristwatch frequencies:

7,200 VPH (semi-oscillations) = 1Hz

18,000 VPH (semi-oscillations) = 2.5Hz

19,800 VPH (semi-oscillations) = 2.75Hz

21,600 VPH (semi-oscillations) = 3Hz

25,200 VPH (semi-oscillations) = 3.5HZ

28,800 VPH (semi-oscillations) = 4Hz

36,000 VPH (semi-oscillations) = 5Hz

43,200 VPH (semi-oscillations) = 6Hz

72,000 VPH (semi-oscillations) = 10Hz

86,400 VPH (semi-oscillations) = 12Hz

108,000 VPH (semi-oscillations) = 15Hz