I recently noticed my Phantom would drift a bit to the right when attempting to fly in a straight line. I did a basic then advanced calibration on a straight level surface, then did a new compass calibration but it still drifted a bit. I tried several different techniques now for calibrating the compass and think I've finally gotten it going straight now but will need to do some more test flights to be sure.
My final calibration involved me holding the Phantom my the landing gear straight in front of me while in a open grass field. With the remote control around my neck held by the lanyard strap I activated the calibration mode. Slowly spun myself counter clock wise 360 degrees till it turned from yellow to green, moved the Phantom facing straight down holding it by the bottom of the landing gear and again, spun in place counter clock wise 360 degree till the lights begun their normal green flash. Again, I'll need to do some more flights to be sure this finally got it going straight but on initial observation it looks better than prior attempts.