Tuning fork

There are two types of tuning fork in mechanical watchmaking:

Metal tuning fork (sound resonator)

Used as of the early 1960s in Bulova's Accutron movement and comprising two metal prongs vibrating at 360 Hz (360 oscillations/second). An electromagnet maintains the vibrations which are transmitted, via a pawl mounted on the tuning fork, to the first wheel in the gear train. Other tuning-fork movements were made with frequencies ranging from 300 to 720 Hz. Tuning-fork watches were discontinued in the mid-1970s when they were replaced by quartz.

Quartz tuning fork (quartz resonator)

Appears as two silicon dioxide (quartz) prongs. The quartz resonator is extremely small and vacuum sealed inside a canister. Quartz's piezoelectric nature causes the resonator to vibrate at 32 kHz. An electronic circuit divides this frequency into a 1 Hz signal in quartz watches with a seconds hand, and drives the stepper motor which in turn drives the hands via gears. This system is now in common usage.