[NoBozo]

If I'm not mistaken, a GPS either gives you a correct and accurate position within a few yards... OR NO Position at all. If the GPS is a handheld and is used with a solid roof overhead (metal blocks the signal) it will likely lose the signal and you will have NO Position until it re-aquires the signal...which may take several minutes.

I have used a GPS inside the house and it will not acquire a signal through the wood walls, probably because of Foil Backed insulation in the walls...BUT it will see the satellites through a south facing window. Sometimes a GPS will lose the signal out in the woods with a tree canopy overhead. Leaves contain water which can block the signal if there is enough of them...then you will have NO Position. NB