During process of checking what could be wrong with my copter I started to test compass.
All test are done on bench (so no GPS fix). Copter 3.5.1.
Internal compass (only one enabled), mag calibration completed with fitness strict, no way to get rid of compass variance error (MP correctly shows world directions).
External compass (only this one enabled), mag calibration completed with fitness default (didn’t complete on strict), no errors (MP correctly shows world directions) unless I rotate copter 90 degress to W, then error is on again and EKF for mag is red and after few seconds display in MP starts drifting to N and EKF went to orange and green. Same story when I turn from W back to N.
How is it possible that copter pointing to W displays N?