vph is vibrations per hour, the standard way of listing how fast a watch ticks. Each vibration is both back and forth, so
- 18,000 vph is 2.5Hz or 5 ticks per second. Quite slow, mostly seen in pocketwatch movements.
- 21,600 vph is 3Hz, or 6 ticks per second. See Seiko 7s26, still quite common.
- 28,000 vph is 4Hz, or 8 ticks per second. This is the current sweet spot for wear vs accuracy. See ETA 2824.
- 36,000 vph is 8Hz, or 10 ticks per second. See hi-beat. Very unusual, very hard to design and manufacture.
Also known as 'bph', for beats per hour.