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Clock, device to indicate or record the passage of time. Generally a clock relies on a source of regular oscillation, such as a swinging pendulum or an electric current. Christiaan Huygens invented what was probably the first pendulum clock in the mid-17th century. The electric clock, commonly found in the home, was invented in the 19th century, and the quartz clock, utilizing the vibrations of a quartz crystal, in the early 20th. The atomic clock, invented in 1948, is accurate to within 1 second in 3 million years. The most common way to display time has been the analogue, with clock hands sweeping over a face, in imitation of the sundial. The most recent type of display is the digital clock, which uses integrated circuits to show the time in changing figures.

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