Whenever I fly as a PreFlight check I always verify my IMU and Compass us not wonky. IMU is usually green and the compass although green gives me a reading between 0 to 90 that fluctuates. Is that ok although it's green. It fluctuates up and down but never really goes yellow or red (upwards). I know a 0 is what we should arrive for but is there documentation somewhere that states what it should be at or what you should never fly if it's X.