2 TWENTIETH-CENTURY NAVIGATING

A series of advances in the 1920s led to the introduction of the quartz oscillator to replace the mechanisms of traditional chronometers.
1
Pendulum clocks typically had one beat every two seconds. Traditional mechanical chronometers used so-called “escapement” wheels that oscillated at two to five beats per second. Quartz oscillators operated in the kilohertz range: thousands of beats per second. When properly calibrated, they offered orders-of-magnitude increases of accuracy.
2
It had been long known that supplying energy to a quartz crystal caused it to oscillate at a frequency determined mainly by the crystal's thickness. Other factors caused the frequency to drift, including variations in temperature, contamination of the crystal, and mechanical shock. One by one, these problems were addressed. By the late 1930s, the US National Bureau of Standards (in 1988 renamed the National Institute of Standards and Technology) was providing time services to the nation with quartz clocks that neither gained nor lost 0.004 seconds a day.