Horizontal Situation Indicators
On the HSI, the airplane is represented by a schematic figure in the center of the instrument. The VOR/ILS localizer is shown in relation to the airplane figure. The heading indicator is slaved to a remote compass-integrating the heading indicator and VOR/ILS (with glide slope). It is frequently interconnected with an autopilot with altitude hold and the capability of following the glide slope all the way to the decision height and beyond.
On a conventional VOR indicator, left/right and to/from must be interpreted in the context of the selected course. When an HSI is tuned to a VOR station, left and right always mean left and right and TO/FROM is indicated by a simple triangular arrowhead pointing to the VOR. If the arrowhead points to the same side as the course selecter arrow, it means TO, and if it points behind to the side opposite the course selecter, it means FROM.