Mine has been doing the same thing for 3 weeks now. I can't get it to stay calibrated. It happened when I brought my computer home, crossed a "zone" border on the way. Nothing in the trunk now except a jack and some stands, so I have no idea what'* wrong with my baby :(

I think the compass is another one of those buggy pieces of GM electronics.
I've driven alot of Bonnie, during my stint at the auto-auction, my time as a parking lot attendant, and as a valet, and I have to say that I believe the greater number of compasses in these cars did not work. The one in my own 95 SSEi never did work right. It always either indicated northwest or asked for calibration.

Yeah, so as I messed up my trunk lock, I realized all my tools are also in my trunk. Large boxes of metal, along with a jack and stands are sure to mess up the compass. Duh. Would go take them all out right now to see if it solves anything, but I'm unlucky enough to mess up anything I think about on this car

hehehe...that'* like 1/2 a shifter ****...