Compass calibration is to eliminate magnetic influences that may cause the digital compass not to function properly. 

Calibration procedure is much easier now than with XP3.1.  The same horizontal and vertical procedure is still the same but with less rotations.  XP3.1 was more sensitive to accuracy in horizontal and vertical leveling.

The GPS' LEDs will let you know when to change to the next step and when the calibration is successful.

Calibration must be done the first time the system is installed and anytime there are any changes made to the helicopter.

Calibrate away from anything that may cause magnetic interference such as cars or steel structures.  Remove any personal items that may be ferromagnetic such as your keys and cell phones.

Recalibrate your GPS anytime you have done any mechanical changes or moved components.

It is not necessary to calibrate for every location you fly at.