Should it show a left-tilting airplane against a fixed horizon, or a fixed airplane against a right-tilting horizon? The first is correct from the viewpoint of someone watching the airplane from behind, where the horizon is always horizontal: this type of display is called outside-in. The second is correct from the viewpoint of the pilot, where the airplane is always stable and fixed in position, so that when the airplane banks, the horizon tilts: this type of display is called inside-out.
