The Horizontal Situation Indicator (HSI) is a combination of two instruments—a vertical Heading Indicator and a VOR/ILS Indicator. The aircraft heading is displayed under the upper lubber line. A course indicating arrow shows the course selected (head) and the reciprocal (tail). The course deviation bar operates with a VOR/LOC navigation receiver to indicate left or right deviations for the course selected. The fixed aircraft symbol and course deviation bar display the aircraft relative to the selected course as though you were above the aircraft looking down. The triangular shaped pointer is the TO-FROM indicator. The glide slope deviation pointer indicates the relation of the aircraft to the glide slope.