

Real-World Relativity: The GPS Navigation System - dhotson
http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

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dhotson
TL;DR.. GPS satellite clock ticks need an accuracy of 20-30 nanoseconds. The
satellites move fast enough that their clocks fall behind by 7 microseconds a
day due to time dilation, but orbit high enough that the curvature of
spacetime due to the Earth’s mass puts them forward by another 45
microseconds. GPS receivers have to perform relativistic calculations to
determine their location.

