The combination of these two relativitic[sic] effects means that the clocks on-board each satellite should tick faster than identical clocks on the ground by about 38 microseconds per day (45-7=38)! This sounds small, but the high-precision required of the GPS system requires nanosecond accuracy, and 38 microseconds is 38,000 nanoseconds. If these effects were not properly taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and errors in global positions would continue to accumulate at a rate of about 10 kilometers each day!
From GPS and Relativity, an explanation of how relativity affects GPS.
I always thought that time dilation was something to worry about when you hurtle yourself across the galaxy near the speed of light. Turns out I was wrong; if you fly on a plane, your life will start going by faster than mine. If you’ll excuse me, I have to go lie down and think about this until my brain returns to a functional state.