Technically there is no compass at all on the gps unit or in arcpad. Correct, it is based off GPS signals when movement is detected. Standing still, the accuracy of the gps unit is directly linked to what is posted on Trimbles site. if it says the unit receives 2-5 meters raw, then satellites will say you are at x, then y, then z, all within a 15 foot circle. thats why the compass in arcpad spins...making navigating back to a point difficult in some aspects.