calibrating compass
So I calibrated my Dynon HDX ADAHRS last night on a Compass Rose.
Question: how accurate do you have to align on the compass rose? I was by myself and drove my RV-7A onto the compass rose aligning with the lines. I used the orthogonal lines to line-up with wing leading edges. At first I thought this was pretty accurate but it seemed like just a spec of brake would move the nose an inch or two which I'll bet is 2 or 3 degrees. So is this alignment really an okay way to calibrate the ADAHRS? I still have to calibrate my magnetometer. It already appears to point correctly. I'm wondering if I'm making it worse with a physical alignment calibration.
Is there a better way to align up with compass headings for calibration purposes? Or is there some magic happening inside the ADAHRS so it doesn't get worse, but better?