10 meters sounds about right for GPS. When I held a GPS unit stationary and plotted its wandering, I found it could vary as much as 50 ft or roughly 15 meters over the course of a day. For smaller intervals the typical wander was significantly less, more like 3 meters to 5 meters depending on the constellation at that time. I never did find out the cause of the infrequent, but much larger wander. Actually "wander" might not be the best term for it. Seems the large deviations were always in some direction and then abruptly back near the center making me think it was some systematic error, possibly calculation errors in the unit itself.