Precision: How a watch works, December 2015

An expert summary explaining the basic functions of a mechanical timepiece

A traditional watch movement is a piece of precision-manufactured mechanical art; utmost accuracy is demanded of it, despite consisting of little more than gears, wheel and springs. To understand how a mechanical movement works, it is best to visualise it as a sequence of events with a start and a finish, a domino effect of power transfer and control along a reactive chain.

It begins at the mainspring, a coiled strip of metal wound within the barrel by either the crown, or – if it is an automatic winder – the rotor weight. The power is transferred through a set of gears, called the going train, to the escapement, which regulates the release of power from the mainspring to stop it unwinding all in one go. It does this by locking and releasing a toothed wheel – called the escape wheel – using the pivoting, twin-pronged pallet fork, which is itself knocked back and forth by the lightly sprung balance wheel. Through clever integration with the escape wheel, the pallet fork is both driven by and drives the escape wheel, the shot of energy released by the mainspring in each beat giving the balance wheel the motion to knock the pallet fork to its next engagement. The regulated power can then be transferred through a set of reduction gears, called the motion work, to the hands, turning each at a speed set by the gearing.

By Andrew Morgan of Watchfinder, the specialist retailer for pre-owned luxury watches. www.watchfinder.co.uk