Aircraft bubble sextant.

Bubble sextant probably made by Henry Hughes and Son Ltd, London, about 1942. Marked on the left side of the casing: [crown] | A.M. | Bubble Sextant | Mark IXBM | Brit. Pats | 480112 490621 | and pending [and] Mod. Inst. 19/99. Marked on the right side of the casing: Serial N° 3260/42. Marked on the averager: [crown] | A M | Serial n° 4564/42. Scale from 0° to 80° every 1°. Vernier to 1'. Black cracle-lacquered alloy casing incorporating artificial materials, housing optical equipment, a clock averaging mechanism, electrical equipment, and two rubber eyecups. Three shades (all red). In a fitted Bakelite case with a leather carrying strap, and containing a calibration sheet and a check list, both dated July 1969.