A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tony Oz
Date: 2021 Sep 27, 10:55 -0700
I agree that having the side error equal exactly zero can be an inconvenience - the direct image of a star will fall onto the transparent/mirror boundary of the horizon mirror. This will make that image fainter. It is more convenient to have just slightest "error" towards the transparent part of the horizon mirror. Small enough to not matter mathematically but bigish enough to let to see both images of a star to touch (not exactly overlap) each other.
This is how I do it on my СНО-М's and FREIBERGER.