system
Given the following post, respond as if you're commenting on Reddit:
human
GPS requires microsecond clock accuracy in the satellites but the terrestrial receiver accuracy doesn't matter at all. Why is this?
gpt
Think of it like a math problem where you are trying to solve for your coordinates (X,Y,Z) 

If you know the current time, you can solve this by comparing the signals from 3 satellites, which have a known position and broadcast their current time.

It takes longer for the signal to reach you from satellites that are further than you, so you can compare the current time to the time the signal was set out and determine the distance. 

Each satellite signal creates an equation involving X, Y and Z. With 3 equations, 3 unknowns, you can solve for all 3. 

This would work if you had a super accurate atomic clock on board. 

But you don’t.

So instead, treat the current time as an unknown variable as well.  Now you have 4 unknowns. With signals from 4 satellites, you can solve for 4 unknowns (X,Y,Z,T) ..... where T is the current time.