GPS relies on precise time measurements to calculate location. Satellites send signals at light speed, and phones measure travel time to determine distance. Each nanosecond of delay equals 0.3 meters, making timing critical. Einstein’s relativity theories are essential: satellites’ clocks must adjust for gravity and speed effects.

Without corrections, GPS would drift 10 km daily. Four satellites are needed to solve for location and clock errors simultaneously. The fourth satellite’s signal helps synchronize the phone’s cheaper clock with atomic clocks in space. Satellite geometry also matters—clumped satellites create inaccurate position ranges. Modern systems use 8-12 satellites for better accuracy. Relativity corrections are baked into hardware, ensuring clocks run at the exact rate despite orbital conditions.

This interplay of physics and engineering makes GPS a global navigation miracle.