A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: John D. Howard
Date: 2019 May 2, 14:03 -0700
You may have what astronomers call a personel error. When several astronomers would time the passage of a star over the ( crosshair ) wire each would have a different time - some early, some late, but would be very regular. They would find out their personel error after many, many nights. Once they knew their error, they would add or subtract the error like an index error.
My own error is one second late. I hit my stopwatch when I see the star on the wire - always late.
You may be doing something simular when you do your sights.
John H. 41N 100W