A mechanical watch is a watch that uses a mechanical mechanism to measure the passage of time, as opposed to modern quartz watches which function electronically. It is driven by a spring (called a mainspring) which must be wound periodically. Its force is transmitted through a series of gears to power the balance wheel, a weighted wheel which oscillates back and forth at a constant rate. A device called an escapement releases the watch's wheels to move forward a small amount with each swing of the balance wheel, moving the watch's hands forward at a constant rate. This makes the 'ticking' sound characteristic of all mechanical watches. Mechanical watches evolved in Europe in the 17th century from spring powered clocks, which appeared in the 15th century.
Mechanical watches are typically not as accurate as modern electronic quartz watches, and they require periodic cleaning by a skilled watchmaker. Since the 1970s, quartz watches have taken over most of the watch market, and mechanical watches are now mostly a high-end product, purchased for aesthetic reasons, appreciation of their fine craftsmanship, or as a status symbol.