How does a mechanical watch work?

A mechanical watch needs neither a battery nor electronics. Its energy comes from a wound spring, its rhythm from an oscillating wheel. In between, more than a hundred tiny components work together. Four assemblies are decisive.

1. The power source: mainspring and barrel

When the watch is wound – via the crown or, in automatic watches, via a rotor – a long spiral steel spring is tensioned: the mainspring. It sits inside a small drum, the barrel, and releases its energy slowly and evenly. How long a fully wound watch keeps running is its power reserve; many movements offer around 40 hours, some considerably more.

2. Transmission: the gear train

The barrel drives a series of wheels, the gear train. It converts the slow turning of the spring so that the seconds, minutes and hours hands move at the correct speed.

3. The brake that keeps time: the escapement

Left unchecked, the spring would unwind in seconds. The escapement – usually a lever escapement with escape wheel and pallet fork – releases the gear train in tiny, even steps. Those steps are the ticking you hear.

4. The heart: balance wheel and hairspring

The rhythm is set by the balance wheel, a small wheel swung back and forth by a very fine hairspring. Every oscillation takes the same time. Many modern movements beat at 21,600 or 28,800 vibrations per hour – 3 or 4 hertz.

Accuracy and care

Temperature, position and mainspring tension all influence the rate, so a mechanical watch gains or loses a few seconds a day. That is normal. To keep friction low, the pivots run in synthetic ruby jewels and are lubricated with special oils. Because these oils age, a mechanical watch needs a regular service.