An Astro (or star) Compass. Mk. II. Used on planes such as WWII-era bombers to determine true heading from the stars (similar, sort of, to the way one would use a sextant at sea). I'm told that these are still in use up north, where navigation by magnetic compass can get complicated. A fascinating device, with spirit levels, adjustments for latitude, declination, etc.
Contains Radium. (20.0 micro sievert/h)