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Frank, you asked

"Why not just make an ordinary table on the pattern that sextants have had for generations?"

That might be the next step, but right now the factor is doing pretty good for starters, and, you just gave me a very helpful simplification for my current approach:

one in 480 means one minute of arc every 8°. So if the sextant reads 24°, the correction would be 3'. By the way, is it up or down?

Thanks, I would not have seen that :)  My sextant reads too high, so I divide by 1.002.

You also suggest that "Doing this in a spreadsheet is needless over-kill, and it is forcing you to think that you require a linear factor." I see your point, and from a message by Greg Rudzinski a few years ago I do understand that it is not necessarily linear, but for now it is allowing me to keep track of my sightings next to the data from your app, and I can play around with the factor that way.

You also write that "The Davis Mk 3 can only be read to 2' precision, so you're done." I am also surprised so far and don't know yet how consistent things will be in the long run, but the fixes have started to get even better now that I am always taking four sightings in quick succession and picking a non-outlier for the fix. See the images I have added.

Thanks for reminding me to "keep in my mind that you are the easiest person to fool." :) I will :) Ah, Feynman, I have the "Lectures on Physics" :) I claim no scientific approach, but do plan to keep track of my sightings for a while. I am also trying to be as precise as possible. And holding the plastic sextant very loose :)

I am including some charts (with the background map and the altitudes removed), this is what I have been getting in the past days. I am not "leaving out the bad ones"---even my earlier fixes were already pretty good in my eyes, too, but I am not including them because I just recently started taking 4 sightings in a row to see outliers. The circle has a diameter of about 1.2 nm. The LOPs / COPs and the circle are not necessarily concentric, the circle is more precise. The star shows where I took the sightings.

Any feedback welcome. I would also be very interested if anybody else wants to put a similar effort into the Davis Mark 3 sightings / corrections and comes up with similar improvements. If simply applying a factor does a lot, maybe others want to try it out? Or do you all think this is a fluke that will go away in a week :) It all started when I noticed that my circles of equal altitudes were always "too close to the sun" (sextant reading too high).

Norman

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