A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: John D. Howard
Date: 2019 Mar 11, 19:47 -0700
I am no expert but in my readings of Lewis and Clark they used an octant with a back sight mirror to get over 90 d. They would use their sextant to get equal altitude sights - they would clamp the index arm and wait until the afternoon for the second shot. Because the sextant was not avaible for the noon LAN they used the back sight on the octant, along with a mercury AH, reqireing more than 90 degrees.
Their octant looks like the very nice one you have.
John H. 41 N 100 W