This astro-clinometer was invented for use by the RAF for night navigation on long-range desert missions during World War II and is one of three remaining examples known to exist. The other two are held by the Imperial War Museum and by a private collector.
The astro-clinometer was invented by E.H. Thompson to be used for night navigation in the desert. There is doubt as to whether it ever went in to service as the same task could be accomplished using a theodolite, a more commonly carried instrument. The astro-clinometer works by measuring the angle of a star without the need of a horizon to measure against. Before use the instrument must be set perfectly level by using two spirit levels illuminated by a shielded lamp.