Astro Compass 6A/1174. Cylindircal flanged base; three knurled levelling screws for circular plate marked 0-360 by 2 degrees; rectangular extension holding two spirit levels and marked 'True Course' with an arrow. Two trunnions and a calibrated worm drive to tilt the circular drum. At the top is an alidade sight lebelled 'declination', which ylits on a horizontal axis 60-0-60. In a wooden box.

A magnetic compass is almost useless at high latitudes, where magnetic variation can be erratic and the angle of magnetic dip can be steep. As flight develped at high latitudes and in the North pole, the military developed the astrocompass to indicate true north when pointing at a known star.