I was just being funny... got a big kick out of the old school way, it's amazing the simple things we forget (stop watch, time and mile markers vs computers and GPS)

How accurate is MPH on GPS? I'm really splitting hairs at this point and don't think ther's an issue, just want a procedure like GPS MPH to verify tire. wheel and gear changes done to bins through software. So far I'm down to 1%. But looking at MPH on laptop to verify would be simple compared to times, miles and math. No biggy...