I have read many 'fly away' posts blaming a faulty or uncalibrated compass as the cause. But what does the compass actually perform for us in the Phantom. I am under the impression that the compass only provides azimuth data that keeps the aircraft pointed in a particular direction, whether its hovering or moving horizontally, until the operator yaws it in another direction. Having used GPS in the desert for 20 years, I have noted that just before navigating to a waypoint, I have to travel a short distance before the GPS knows my motorcycle's azimuth or orientation. The GPS can't tell the azimuth of the aircraft in a hover, until the craft has moved horizontally over the earth for a short distance. HL is a good example of this in action. In HL, the orientation or azimuth of the aircraft is ignored and the GPS uses its data to bring the craft back to home point. So, IMO, blaming the compass on a 'fly away' is incorrect. Maybe those that know the workings of the NAZA controller and compass can chime in and help explain.