Thanks for that... To answer, first, I see servo slips fairly often in both alt and hdg/gts in choppy air with both servos set to 100% especially if there has been a serious jolt or something where a large correction order is sent. Second, I just redid the calibration prior to the last flight I made before writing that input. So I don't think I can do it any better. Taxiing straight ahead on the ground, my GPS track on the GNS 430, pretty much matches the heading on the D10A, and both even return the same runway heading going down centerline as published on the airport diagram detail on NACO charts. It's different in the air but very difficult to determine what is actually causing the heading disparaties. Today I was out in bumpy air heading south hand flying the airplane and I could lock the D10 heading fine. But when you turn on AP, heading wanders...today about 10 degrees. I may have been wrong yesterday. AP could be doing all the dirt. I'll keep trying to nail it down and keep you informed. Could be the magnetometer for that matter. Lets see what happens...Jack L
Sorry to be uncertain.