NavList:

George H, you wrote:

"Take "using corrections with the wrong sign". Well, if you applied the
refraction correction with the wrong sign, it wouldn't make much difference
for high-altitude objects, but would systematically put lower bodies into
the wrong place."

 

Sure. Obviously it can only work with those altitude corrections that have the same value for all sights. And those are index correction and dip (and semi-diameter, too, if you're doing a running fix with Sun sights). But here's an interesting way you could use the graphical method Peter has posted. You're quite correct, of course, that we don't ordinarily know that there is a systematic error, and there's no way with just three sights to disentangle random errors from systematic errors. But suppose we intentionally have a systematic error. Imagine this; I take altitudes of three stars, and I correct them for refraction. Now I simply ignore IC and dip and plot LOPs. Why would I do this? I'm sure I could invent some hypothetical scenario where it might be necessary in a "practical" case, but let's just say I'm leaving out the corrections because I'm lazy today and I want to save myself the effort of doing six additions/subtractions. Instead, I plot my triangle and do the graphical trick. I've traded six additions and/or subtractions for some plotting to achieve practically the same result. If nothing else, it's a neat alternative.