Power reserve, frequency, amplitude and beat error

When a mechanical watch comes into our workshop, it is first placed on a timing machine. Four values quickly reveal its condition.

1. Power reserve

How long the watch runs when fully wound. Many movements offer around 38–50 hours, some several days. If the power reserve becomes noticeably shorter, this often points to aged lubricants or a tired mainspring.

2. Frequency

The number of balance oscillations, stated in vibrations per hour (vph) or hertz. Common values are 21,600 vph (3 Hz) and 28,800 vph (4 Hz). A higher frequency can make the rate more stable against small disturbances; a lower one reduces wear.

3. Amplitude

How far the balance swings, measured in degrees. With a fully wound watch lying dial up, a healthy movement usually shows a clearly high amplitude – often around 270–310 degrees, depending on the calibre. A low amplitude is a typical sign that a service is due.

4. Beat error

Measures whether the tick and the tock are equally long, in milliseconds. A small beat error is normal; a large one makes the rate less stable and can be corrected during regulation.

And the daily rate?

The rate – seconds gained or lost per day – is measured in several positions. It results from these values together. Tolerances depend on the movement and the manufacturer.

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