A Bubble sextant

I am selling a bubble sextant

navigation instrument . Used for aircraft navigation in World War II

A normal sextant is unsuitable for

use in an aircraft because the horizon is not level with the observer as in a

ship, so the bubble sextant was developed for aeronautical use in the 1920s. It

was very important in WWII. The automatic averaging atachment was meant to

ensure that unbiassed measurements were made while the bubble and observer

wobbled randomly, so that the error would reduce as the square root of the

number of observations. Sixty measurements were averaged as the observer tried

to keep the bubble and a star in coincidence for a two minute period.