A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2016 Dec 20, 23:10 -0800
Measuring index error should be done with a scope. The higher the power the better. The range differences shouldn't be more than 0.4' for a set. Your 0 to 2' range of index error is too much and indicates that something is wrong.
Practicing cellnav is an iterative process. Get something to a reasonable standard and then move on to other things. Then go back and improve the processes.
When I started taking sights my sextant had a large side error. I eliminated most of it but did not spend time getting rid of it completely because there were other things I was trying to get right. Maybe now is the time to work on side/index error again. Something to do in the hours when the sun's altitude is greater than 60°.
I suspect that I am sometimes careless when measuring IE - I do not read the vernier as carefully as I should because I perceive that I am wasting "sun time". I would rather be taking sights. But of course accurately measuring IE is as important as taking accurate sights.