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Panoramic view of the clock hall at PTB with the four caesium clocks CS1, CS2, CSF1 and CSF2.

Is the second a special unit of measurement?

quot;Is there anything in the world of technology which has made a special impression on you?" the F.A.Z. recently asked Professor Dr. Hans Küng, the theologian. His reply: "My radio-controlled alarm clock which switches to summer time on its own." And right he is: Not only in March and October when we switch to summer and winter time, respectively, is the radio-controlled clock right on time. For the second is a special unit. It is the only one of the seven base units which is available in Germany to anyone at any time, realized in the best possible way. By emitting the time signal via the DCF77 long-wave transmitter (controlled by PTB's atomic clocks), the PTB fulfils the obligations imposed on it by the 1978 Time Act. The radio-controlled clock thus is the most precise measuring instrument in everyday life.

While kilogram, metre, kelvin, mole, candela, and ampere can be accurately determined only with well adjusted measuring instruments, the comparison of clock settings in everyday life is a thing of the past. This has yet another advantage: This omnipresent, precise unit of measurement allows many derived units to be easily determined in everyday situations. The distance of a thunderstorm, the speed of an athlete, or the acceleration of a motor vehicle, for example.

By the way: If your alarm clock is displaying the wrong time despite all that, the reason usually is a malfunction of the clock or an empty battery and not the time signals transmitted. There has been no incorrect transmission since 1970.