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.