Electronic crystal clock

The only continuous time signal service is provided to the world by the National Bureau of Standards. One or more of the broadcast frequencies (5, 10, and 15 megacycles per second and 2.5 megacycles at night) is being used continuously. A crystal clock, utilizing electronic circuits instead of the conventional clock mechanisms, has been developed to insure accuracies to within a microsecond for use in navigation, seismology, and geological surveys. The flawless quartz crystal, the heart of the circuit, has a resonance frequency of approximately 100,000 or 200,000 cycles per second, and is sealed in a glass or metal enclosure to insure against variations in pressure and humidity.