When it comes accuracy of the digital compass in the XRX, the unit was designed to operate in an aircraft. And the magnetic fields surrounding an aircraft are far different than those around a car. So calibrate it in your plane, while pointing due north with your wet compass. We recommend you do this on the ground, simply because while you are flying your attention should be on your flying your plane.

You should only have to calibrate the compass on the initial setup, this allows the digital compass to adjust to your aircraft. However if the unit is exposed to strong magnetic fields then a recalibration may be needed.

Thanks

Daniel