Also known as “A/h” or “Alternance per hour”. 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. In a watch movement with a balance wheel, one vibration is a single swing of the balance wheel. A vibration is one-half of an oscillation, or a semi-oscillation. So, one swing of the balance wheel in either direction, for example clockwise, is one vibration or semi-oscillation, and two swings, for example clockwise then counter-clockwise, is an oscillation. Read the full explanation at Vibration or vph.
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