How does GPS work?
The science behind GPS
Now that you know how GPS has been developed, it's time to dive deeper into the subject and find out exactly what happens before your navigation device tells you exactly where you are.

The location of the satellites
To work out where you are, your navigation device needs to know two things: a. The location of at least four satellites above you, b. Your distance from each of those satellites.

The distance of the satellites
A navigation device works out its distance from a GPS satellite from the time it takes the signal to travel to the receiver from the satellite.

The fourth satellite
In satellite navigation perfect timing is everything; the fourth satellite checks the time measurement of the other three satellites to make sure the information about your location is as accurate as possible.

Atmosphereinduced error & Multipath error
So we’ve got perfect timing and we know the satellite's exact position. But up to now our calculations have been based on the speed of light in a vacuum, the only place where the speed of light is a known constant.