Clock Correction

the difference between the exact time at any moment and the clock reading at that moment. A clock correction indicates the number of hours, minutes, seconds, and fractions of a second it is necessary to algebraically add to a clock reading in order to obtain the exact time. Clock correction can be found by reference to sidereal or mean solar time, either local, standard (zone), or universal. Calculation of clock correction is one of the basic problems of practical astronomy, and time services conduct routine astronomical observations to determine such corrections. The clock correction changes over the course of time; this change in the course of a single 24-hour period is called the diurnal clock rate.