NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Peter Mackenzie
Date: 2025 Jan 20, 13:33 -0800
Hi
I have been given a Cooke sextant. I am not sure it works correctly, (or maybe it's me!).
The problem is this: with the arc and micrometer both set to zero, when I look at the sun (with shades), I can adjust the side error and index error screws (both located on the horizon mirror) so that both suns appear on top of each other. However, when I simply move the sextant to look at the distant horizon, there is clearly a lot of index error present as the right half of the horizon is far higher than the left half. Similarly, if I then adjust the two screws on the horizon mirror whilst looking at the horizon, and get the horizon object perfectly aligned (eg: to a distant light house), with no side/index error, but then look at the sun, the two suns (through index and horizon mirrors) are way out.
I wonder what type of error this is?
