It's a position indicator that shows your heading relative to the controller. If your device does not move for a while, it will sleep the compass. All that is required is to move it and it will reacquire. If your device doesn't have a built in compass, like some tablets, it usually never works (or so I've seen posted). I use my phone and as soon as I move it, the red indicator goes away. Not always the most accurate but it's no longer red. Doesn't affect the flight characteristics whatsoever. Like others have suggested, use the map to get your orientation status.