The time correction DUT1 (sometimes also written DUT) is the difference between Universal Time (UT1), which is defined by Earth's rotation, and Coordinated Universal Time (UTC), which is defined by a network of precision clocks.
UTC is maintained via leap seconds, such that UTC remains within the range −0.9 s < DUT1 < +0.9 s. The reason for this correction is partly that the rate of rotation of the Earth is not constant, due to tidal braking and the redistribution of mass within the Earth, including its oceans and atmosphere, and partly because the SI second (as now used for UTC) was already, when adopted, a little shorter than the current value of the second of mean solar time.^{[1]}
Forecast values of DUT1 are published by IERS Bulletin A. Weekly updated values of DUT1 with 0.1 s precision are broadcast by several time signal services, including WWVB.

