he REALACCEL numbers are calculated with respect to the orientation of the sensor itself, so that if it is flat and you move it straight up, the "Z" accel will change, but if you flip it up on one side and move it in the new relative "up" direction (along the sensor's Z axis), it will still register acceleration on the Z axis. Essentially, it is sensor-oriented acceleration which removes the effects of gravity and any non-flat/level orientation.