Watches are used to measure and display the time. The movement is the central component of mechanical watches. Chronometers are watches whose mechanics have a certain degree of accuracy. Radio clocks regularly carry out an adjustment with the time signal transmitter DCF 77. Early elementary clocks as well as optical numerical displays, on the other hand, operate without moving parts. From wristwatches to wall clocks, alarm clocks, kitchen clocks to electric clocks, many variants are available.