Sensor playoffs
Since this is measured off the human body by strapping the phone, we need to consider 2 basic start orientations of the human body: Standing and resting or sleeping. In the standing start, the device if strapped parallel to the vertical (standing) axis of the body shall show the angle as either 0 deg or 180 deg. In the sleeping start, if the device is parallel to the horizontal (sleeping) axis of the body (and is also parallel to the ground) then the angle is again 0 or 180 deg.