====== Vibrations per hour ======
The [[balance]] of a watch oscillates at a predictable rate, typically referenced as **vibrations** or **alterations per hour** (**A/h**) or **hertz** (**Hz**).

===== Overview =====
One vibration ("semi-cycle" or "beat") is a movement limited by two end positions. So the [[balance wheel]] of a watch may makes eight semi-cycles per second, which is 28,000 per hour. This is often divided by two and counted in hertz (Hz). Thus, a 28,800 A/h movement moves at 8 semi-cycles per second or 4 Hz.

The number (frequency) of the vibrations of the [[balance wheel]] is determined by the diameter and the weight of the balance wheel and [[hair spring]]. The higher the frequency, the greater the reduction to the [[gear train]] must be.

Typical watch oscillation rates:

^A/h ^  Hz^  V/s^Notes ^
|18,000 |  2.5|  5|Typical pocket watch|
|19,200 |  2.6|  5.2|Faster pocket watch|
|21,600 |  3|  6|Classic watch|
|28,800 |  4|  8|Classic "high-beat"|
|36,000 |  5|  10|Modern "high-beat"|
|72,000 |  10|  20| |

===== See Also =====
  * [[High-beat]]
  * [[Rate]]


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