A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2020 Jan 30, 17:36 -0800
16 minutes of arc! That's a huge error, and it should be yelling at you "something went wrong!" I opened your spreadsheet. I looked at cell H27. And... wait, that says 38.3' which matches what we see looking at the graph, right? So... problem, right?
Within minutes of the same time, while you were shooting a Venus lunar up there on the New Hampshire coast, I was shooting a Venus lunar from my backyard here in Rhode Island. I don't have the details in front of me right, but the net error was +0.7'. It's a recently-acquired sextant, not completely adjusted, and I'm hoping for improvement.
Incidentally, you said that you are using "43° 00.0 N, 71° 00.0 W" for your DR input. You may be taking the label "DR" in the web app too literally. You should input your best position there. If you're using the app just for testing yourself and your sextant, then you should feed in your actual position. You can then experiment to see if changing the DR by a few minutes will make any difference. It won't because the process is insensitive to uncertainty in the altitudes. Your "DR" position can be wrong by 5', and in most cases this will have a negligible effect on the clearing process, and even less so if you provide observed altitudes.