Regarding measurement. I may be wrong but I understand that increasingly GPS is used to survey courses and tracks to determine distances. It may be used to survey a record course covering several miles (Bonneville? Black Rock? Lake Gairdner? I don't know) It is an accepted method, but is it accurate? It is accepted as such, but is it really?
Sometime ago, I read on this site someone questioning it too.
A few months ago, I was having a conversation on the subject with a civil engineer whose company builds long span bridges, and his opinion was that GPS is not too accurate, and certainly not foolproof. He was quoting me the recent case of a 1.6 km bridge (that's a mile!), measured by GPS on 3 different days, by the same surveyor with the same equipment, giving discrepancies up to 6m.
So, even without deliberate cheating, you can have inaccuracy to start with, even on permanent sites.