The global and uniform basis for the determination of time is disseminated by the International Bureau for Weights and Measures in Paris as UTC (Coordinated Universal Time). It is realized with the assistance of seventy time institutes, among these also the Time and Frequency Department of PTB. Since our everyday life – despite atomic clocks – now as ever follows the position of the sun, the atomic time scale (realized by atomic clocks) is occasionally adjusted with leap seconds to the Earth's rotation which is not uniform in time. The atomic second is on an average somewhat shorter than the calculated second of the mean solar day. Since 1.1.1958, a time difference of 34 seconds has accumulated up to now: The clock designated as TAI (Temps Atomique International) is, in comparison to the clock designated as UTC, 34 seconds faster. Central European Time is thus UTC + 1 hour, Central European Summer Time + 2 hours.
In the night of 1 July 2012, the last leap second was inserted. At 01:59h 59s CEST, the second with the designation 01:59h 60s will follow and then 02:00h 0s will be reached.