First quartz clock

The first clock to use a quartz-crystal oscillator to generate a time signal was built at the Bell Telephone Laboratories in New York City, USA, in 1927. Two Bell Labs researchers, Warren Marrison and JW Horton, had been working on quartz-crystal oscillators and related technologies since late 1924. It is not clear exactly when they made the clock, but it was first shown to the public at an academic conference in October 1927. The clock used a quartz crystal that oscillated at 50,000 Hz, and this signal was then converted by a frequency divider into a usable clock reference.

Quartz-crystal timepieces make use of a phenomenon called the piezoelectric effect, which was discovered by the brothers Paul and Pierre Curie in 1880. They found that certain crystals generate a small electrical current when subjected to mechanical stress (i.e. when they're squeezed or twisted). Inversely, these same materials rapidly expand and contract when exposed to an electrical current.

Researchers in the early 20th century discovered that the frequency of these cycles of expansion and contraction (known as oscillations) was extremely consistent, but could be varied (or tuned) by shaping the crystals and the attached electrodes. It was also discovered that the electrical pulse generated by the crystal could be amplified and then fed back into it, keeping it oscillating at the exact same amplitude and frequency indefinitely.

Marrison and Horton had been working with electrical timekeeping systems (which used metal tuning-fork-like oscillators) since the early 1920s, but were not satisfied with the low frequency of the clock signals (between 100 and 1000 Hz) and these systems' susceptibility to outside influences.

They turned to quartz in the mid-1920s, and crucially developed a frequency divider circuit that enabled them to transform the high precision oscillations of a quartz crystal into a usable clock time signal. They refined this design considerably with their second clock in 1928, and by 1929 quartz oscillators were being used to generate time reference standards in several countries.

A modern quartz oscillator (the sort of simple and cheap design that is used in everything from wristwatches to computers) typically oscillates at 32,768 Hz and will generally only drift by around 15 seconds per month.