This is a small marine octant with a Willson bubble telescope, a Fischer
rapid release lever, a drum micrometer, an electric light over the divided
scale, and a battery in the handle. It was designed by Victor Carbonara, a
talented engineer from Italy who realized that aviators never measured angles
greater than 90 degrees, and so could use an octant rather than a sextant. And, since aviators did not need the accuracy required on shipboard, they could make do with instruments of much smaller size.
Piero Bonelli used this instrument in 1928 when he attempted to fly from New York to Rome. His widow donated it to the Smithsonian in 1976. The serial number indicates that this was the 7th example of the Model 206.
Ref: R. W. Willson, "Instrument Including Means for Determining the
Horizontal Direction," U.S. patent #1,705,146
Pioneer Instrument Co., Pioneer Instruments and Equipment (Brooklyn, ca. 1930).