It is possible to utilize any device that is able to produce a series of constant distances in time as a clock. The best time-setting scales available today utilize quartz crystal fluctuations or atomic state transformations. In surveying and navigation, these time scales should be linked to the Earth's time. However, the topo-centric distance of a satellite is directly related to the Earth's rotation, which in turn is a function of time. Since the atomic clocks produce independent time scales, there is a need to align these times. This is the task of the Earth’s rotation and those involved in time service affairs.