NavList:

Martin Lechler you wrote:  I wonder whether it would be possible to employ the pentaprism to take "over the shoulder" sights?

What a great idea, thought I.  E.g., shooting Polaris while lining up on Mintaka; shooting the sun while lined up on with your shadow.  Then I started to think about it in more detail and decided it might not be that easy.  How would you hold your sextant?  Unless you had a rubber neck, you’d have to lie on your back with your legs apart and aim the pentaprism between your feet.  Alternatively, you could turn your sextant upside down, but that would rule out Sun shots, because the pentaprism has no shades.  Nevertheless, it would be worth trying on a clear night with a portion of the horizon remaining discernible.  DaveP