If you look at the picture you see how I have mounted the external compass and GPS. The arrow the the direction it should be mounted. However I have not followed the direction because the wires come out of the left side of the module.
Ofcourse the compass direction is wrong now. If I point the nose north the direction it gives is not north.
How can I change this? By the way the APM itself is upside down so I have set AHRS_ORIENTATION to 8. The APM itself is pointing the correct way. The artificial horizon is correct.
So, I should correct the magnetometer readings. But how?