Relativity at GPS scale: why satellites are clocked slow on the ground
GPS satellites carry atomic clocks that are deliberately set to run slow on the ground so that relativistic effects in orbit bring them to the correct rate; special relativity would slow moving clocks by about 7 microseconds per day, while general relativity would speed them up by about 45 microseconds per day, for a net gain of roughly 38 microseconds per day that would cause ~10 km of positional error daily if uncorrected. The main correction is a ground-based frequency offset (about 10.22999999543 MHz instead of 10.23 MHz) so the clock is right in orbit, with smaller orbital variations corrected by the receiver.
