Oh man, when I was a kid piloting a 60ft Boat at night, I was always off course because of the wind and tide moving, which throws you off course. I was always making corrections using channel markers to put me back on course. Even though my Compass is flat, the movement is rotational, just 5 degrees off course will throw you miles from your destination. A jet going at higher speeds and higher altitudes means just a few minutes and you'll be off course big time !

ohhh the truth hurts.