A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Modris Fersters
Date: 2020 Nov 26, 11:06 -0800
Hi, Jim again!
As I understood you checked side error and realised that this is not the reason of the problem. I only wanted to show by example (see picture below) that it is not true that side error is inessential.
Side error of 5’ will cause SD error 0,2’.
My next guess on the subject of your problem is following: maybe when you measured the angles, the altitude of the Sun was low (for example, 10 degrees). Contraction of the semidiameter simply can induce the error in SD. In such a situation it is a good practice to hold sextant horizontally (then SD will be not affected by contracted SD).