This simple plastic instrument has open sights on one side and a bubble
level on the other. The rim is graduated every degree, in four quadrants. It was made for the Navy Bureau of Aeronautics in the mid-1940s, and donated to the Smithsonian in 1972.
Ref: U.S. Navy. Bureau of Aeronautics, Pocket Bubble Sextant (1944 and 1946).