Today I began instrument lesson number 21: reviewing (without outside references) stalls, slow flight, and steep turns, and practicing partial panel flight (without an attitude indicator or heading indicator). This lesson should be called, “How to Use the Magnetic Compass, the Instrument You Forgot Exists.” I had practiced partial panel flight on the simulator twice. But our simulator doesn’t simulate compass errors caused by the idiosyncrasies of the earth. Now it was time for the real thing. Depending on what you’re trying to do, the compass might sit still while you’re turning, turn in the wrong direction, indicate you’ve reached a certain heading when you really haven’t yet, and more. But there are rules to the way it works so you always know how to deal with it. I had always read about these things but never paid much attention to them in flight. I was surprised because the compass errors were more drastic than the books made them sound. I learned some useful things today. On my next lesson, I’ll take things a step further and do partial panel instrument approaches.