Why Your Map App Isn't Off by 10 km a Day: The Clock Fix Hiding in Your Pocket
Your phone's location depends on the clocks aboard GPS satellites 20,000 km overhead. Relativity makes those clocks run 38 microseconds fast every day, enough to throw your map off by about 10 km if nobody corrected it. So engineers build the satellites to run deliberately slow before they even launch. Einstein, it turns out, helps you find your way every single morning.