A mechanical pendant watch is a watch that uses a mechanical mechanism to measure the passage of time, as opposed to modern quartz pocket watches which function electronically. It is driven by a spring (called a mainspring) which must be wound. 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. Mechanical pendant watches evolved in Europe in the 17th century from spring powered clocks, which appeared in the 15th century.
Mechanical pendant watches, like any mechanical device, can vary greatly in their accuracy and reliability. They are often worn for their aesthetic attributes, as a piece of jewellery and as a statement of one's personal style.