This Air Ministry Astro Compass MkII was used during WWII on Lancaster Bombers.
It was part of the carry-on kit which aided airmen to determine the direction of true north by using a variety of astronomical bodies. This was particularly useful when flying in polar regions when magnetic compasses were unreliable.
To use the compass, the base plate is levelled with the horizon and pointed North. The equatorial drum is then tilted in relation to this base according to the local latitude. The sights are then set using the local hour angle and the declination of whatever astronomical body is being used. Once these settings are made, the astro compass was turned until the astronomical body is visible in the sights. It will then be precisely aligned to the points of the compass.
Still in the original box - note that the lid of the box has come off its hinges. see photos for details of condition.
A copy of the instruction manual is provided with this item.
The item appears to be complete but has not been tested. The levels and sights can be adjusted using the various dials etc.
A really interesting collectors item or desk ornamental piece.