You may have noticed that the displayed image becomes a trapezium if the projector is tilted up or down. The projector has a tilt sensor. When you tilt the projector up or down, the projector will measure how much it is tilted. Based on this measurement, the projector can apply a correction so that the picture is always straight on your wall (or ceiling).
This feature is only about up/down tilt correction. To correct for left/right angle, use the "4-Corner Correction" feature.