Physics and measurement of time
Quartz crystal
Also: quartz
A quartz crystal vibrates at a very stable frequency when an alternating voltage is applied, thanks to the piezoelectric effect. This vibration is the time base of virtually all electronic clocks, from wristwatches to network equipment.
Quartz is cheap and reliable but temperature-sensitive; compensation (TCXO) or a heated enclosure (OCXO) increases the stability for demanding timing applications.