I have Maksutov Cassegrain and it suffers from "mirror flop." I.e. when you look at something low in the sky, the focus changes when you swing it to something higher in the sky. Thus a constant need to refocus arise when you change the angle of the scope.
The RPI-1031 employs the principle of ROHMs advanced photo interrupter technology through the integration of one IR LED and two IR photo transistors. It allows identifying the gravity direction in equipment turning up, down, left and right.