H. Hughes and Son Mk VIII Sextant
Standard RAF issue in the 30's and
still used for training purposes after the MK IX had been introduced in 1940.
Note the pencil, used to achieve
an average indication as many American Instruments did.
The photo above, from a wartime
book, shows apparently, Pilots being trained in sextant use.
Whilst I am not certain that the German
firm Plath did actually copy this instrument, there are remarkable
similarities in their instrument, even down to the helix with
a cam follower for the index mirror. I have not opened mine yet
but will have to eventually because of a lack of bubble. My Plath
Gyro Sextant I have had mostly in pieces and think I fully understand
the function of its parts.