'Synclock' electric motor clock, 1931.
© Science Museum / Science & Society Picture Library
This is an example of the first type of synchronous motor clock to be marketed in the UK. A synchronous motor runs at a speed proportional to the frequency of the AC power supply driving it, so if the frequency is fixed such a motor can operate as a clock. Synchronous motor clocks were first introduced in the USA in 1918 and in the UK in the 1930s, and remained hugely popular as domestic timekeepers until the advent of the quartz crystal domestic clock in the 1980s.