So I'm doing a report on special relativity and GPS and kinda at a loss what to do: 1. I've actually found several sites denoting the need to calibrate for relativistic effects when calculating locations, and I'm writing a report on just the opposite, that how is the system effected / how much difference does it make. So which should I believe? My Physics / Math teacher or for example, this guy: < link to crackpot site deleted by Doc Al > 2. If I am to prove that it has an effect, what equation should I use to see the diffirence? Should I use: t^1 =γ ((t - v*x)/c^2 ) x^1 =γ (x - v*t) where γ is Lorentz factor. Thanks in advance. PS: Sorry for any Typos, English aint my first language.