A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Date: 2018 Nov 19, 09:37 -0800
Perhaps this drawing from the manual - attached - can help.
I do recommend the book
THE SNO-T SEXTANT
(with notes on the Freiberger Drum sextant)
by W. J. Morris.
See also NavList RESOURSES, Bill Morris Sextant Blog.