Originally Posted by
williamskg6
Depending upon satellite geometry and the number of satellites 'visible' at the time of observation, an un-augmented single GPS receiver can only deliver accuracies with around 10-30 meters.
But fortunately the bias errors like you describe are highly correlated in time, the error changes slowly with time. Thus while the absolute measurement may be off by 30 meters, they are all off by the same amount. Thus distances computed by successive differences are much more accurate than the 30 m bias number would suggest.