File:ILS gauge.svg

English: This is a simple Instrument Landing System on-board gauge.

The vertical needle indicates the horizontal position of the localizer beam, in this mode the scale is notched by 1 degrees. At this case the airplane is about 1.6 degrees right of the runway center line. The real measure of the deviation depends on the distance from the ILS zero point.
The horizontal needle indicates the position of the glide slope beam, the scale is notched by 1/4 degrees. This instrument is four times sensitive for vertical deviation which is more difficult to detect by naked eye. At this case the airplane is about 0.2 degrees under the optimal descend line now.

There are other types of ILS indicators but this configuration is the basis of most.