GRT Magentometer calibration

Has anyone have their heading/magnetometer calibration change?

I have been flying with it in my RV-9A for 3 years and the heading always made sense. Since the last AHRS upgrade, I did a re-calibration of the magnetometer. It hasn't been correct since. The best I can do now is it shows 15-18 degrees more than it should in all directions.

Could I start the calibration at 345 degrees instead of magnetic north to compensate?

I upgraded to .39 and did not re-calibrate my magnetometer but have not noticed any issues, though only one flight has been made since.

I will pay attention to it on my next flight to see if there is any discrepancy

I have made all the AHRS upgrades, over the past year on my SHS and SSX units, never recal'd the magnetometers afterwards, and the heading is still accurate.

Don't mess with success....

If you do the calibration with the canopy open and have the magnometer near the canopy with it open it will cause that, found out the hard way, also done mine with everthing on and engine running and taxing in a circle

Last night I made sure the canopy was closed. The first calibration the error improved so that it was 10 degrees off. So I did it a second time and it is within 5 degrees!

I had problems with this with AHRS version .35, the turn and bank was "rolling" and the heading was off by a large margin. I did a magnetometer calibration then and it didn't help. I took the unit into GRT and they came out with AHRS version .39 that fixed the turn and bank. The best I could get the heading was 10 - 15 degrees.

Is it possible because of the problems earlier, it took several magnetometer calibrations to work itself out?