Compass Calibration aka dance with the Phantom, we've all done it but why? There are many theories out there ( including my own ) but I want some real facts not guesses as educated those may be

A. What's behind the compass calibration?
1. Is it just to make corrections for magnetic interference around the magnetic compass (horizontal turn)?
2. Is it also determining the nose position in relation to the compass (vertical turn)
3. ....what else please, specify?

B. Which components on the Phantom are being calibrated when we do the compass cali?
1. The magnetic compass module?
2. Level sensors?
3. Inertia sensors / Gyros?
4. ...other, please specify ?

C. What would happen if the magnetic sensor north is off by a few degrees?
1. Unstable position hold?
2. J-hook or toilet bowl pattern?
3. Not much?
4. ...what?

D. What would happen if the magnetic sensor north is off by 180 degrees after calibration (e.g. calibrating with very large magnetic interference in the area)?
1. Can't happen, it would be detected and create a compass error?
2. Not much?
3. The unit would take off never to be seen again?
4. ...?

E. What would happen if a large magnetic interference that throws the magnetic compass off is encountered in flight (e.g. flying close to a large metal structure, mountain with magnetic rocks,...)?
1. unstable flight?
2. unstable hold?
3. loss of control?
4. Error, autoland?
5. bye bye Phantom?
6. ...?

F. For which flight modes is the magnetic compass information used/important?
1. GPS-Atti hold?
2. GPS-Atti flight?
3. Atti only flight?
4. Manual flight?
5. Waypoint flight?
6. RTH?
7. IOC HL?
8. IOC CL?
9. ...?

Thanks in advance for some facts on this

compass calibration make corrections for magnetic interference around the magnetic compass in 3-D space. during flight, we have good algorithm to eliminate the influence of compass interference. so if the magnetic sensor north is off by a few degrees, it maybe have a J-hook when hold, but  after a feel time flight, it will keep stable.

DJI-Andy Posted at 2014-10-16 21:14
compass calibration make corrections for magnetic interference around the magnetic compass in 3-D sp ...

Thanks for your answer.  
I guess you are talking about Magnetic declination.  So does it "learn" the magnetic declination by comparing magnetic compass change values vs.  GPS location values and / or does it use an internal database/calculator for location specific declination and " fine tunes"  from there?   
Does it do this magnetic declination correction only after a compass calibration or is this something that is done constantly and being fine tuned while stationary in GPS mode?
P.S. I'm still eager to know when the electronic magnetic compass is actually being and when not ;)

the declination correction is running real time during flight when there is enough gps, no matter which flight mode

DJI-Andy Posted at 2014-10-16 23:04
the declination correction is running real time during flight when there is enough gps, no matter wh ...

Thanks Andy,
more questions though, is that correction stored in non volatile memory or is it lost every time when the Phantom is powered down?
If it is stored is it then being "reset" when the compass calibration is done?
Is it also doing correction for magnetic inclination (angle of magnetic field in relation to the ground) while flying or is it only doing that during the calibration dance?

Clarification regarding my question about compass and flight modes,  what I want to know is when is the compass data used by the Naza-M controller, e.g. is the magnetic compass used in Atti mode to hold the orientation or not?  

I know it's many questions and I hope I'm not asking for any DJI secrets here ;)

Just a little onetime push to the top to see if any more answers from DJI are forthcoming