Garmin extrex10 + compass

GPSs use two different compasses, some have what is termed an electronic compass while others just have a 'GPS compass', they work in very different ways, the Etrex 10 does not have an electronic compass.

With an electronic compass the unit actually detects the earth's magnetic field, this type can be used either while the GPS is moving or standing still as long as it is calibrated first, it is the better of the two compass types

If, like your Etrex 10, the GPS does not have an electronic compass it can still display a compass screen BUT there are limitations, the biggest of which is that the GPS must be moving, it can't determin where north is when it is in the same position, this is because the GPS needs to compare your current location with a past location in order to calculate if it had moved North, South, East or West. So changing direction while moving can be detected but facing different directions while standing on the same spot can't be detected at all