Guides · The movement

How an automatic watch works

An automatic watch has no battery. On the back of the movement sits a half-moon-shaped weight, the rotor, which swings when your arm moves, and through a small gear it winds the mainspring. The spring releases its power slowly through the gear train to the escapement (the pallet fork and escape wheel), and the balance — the small wheel that swings back and forth with its hairspring — divides time into equal slices. It is the balance you hear ticking.

A fully wound spring keeps the watch running for the power reserve (most automatic movements have 38–42 hours, some 70–80). If the watch lies still for longer than that, it stops — then you wind it at the crown and set it; it is not a fault. An automatic watch with a visible movement (a display case back — it says so in the product's specifications; skeleton watches show the whole movement) lets you watch the rotor and balance at work.

If you have a question about a particular watch, ask Nord, our assistant, at the bottom right — or write to us.

More guides about the movement

The movementHow a quartz watch worksA quartz watch runs on a small battery. The movementWhy does an automatic watch cost more?An automatic movement is around 150 parts that have to be assembled, oiled and adjusted; a quartz movement is a circuit board and a small motor that are mass-produced. The movementWhat is power reserve?The power reserve is the time a mechanical watch runs, from the mainspring being fully wound until it stops — without being touched.