NavList:

Bob B., you wrote:
"I'm using the inverse of Intercepts as a weighting factor. And not doing decimal minutes for the Fix. Star B and C intercepts roughly the same to each other but 15x longer than the Star A intercept. So, I think the Star A sight (and LOP) has more weight to me."

I think I understand how you came up with this, but, first thing first --no, that's not a good idea. :) Instead, just look at the triangle made by the three lines of position alone. Where would you put your fix based on the shape of that triangle? I added the specific intercept distances and azimuths for each sight primarily because "standard procedures" for this process (like those found in the back of the Nautical Almanac for over 35 years!) require them.

The reason your logic doesn't fly is something fundamental to the idea of the "intercept" lengths and the intercept method itself. Namely, the position of the reference point from which we do our calculations, and hence the place to which the intercepts are referred, is fundamentally arbitrary. I imagine that you were thinking of the reference point (the assumed position, or AP, as it's called) as our true position, or at least our best estimate position. If that were the case, then long intercepts might seem to imply relatively lower quality sights... But that's not true. The AP or "assumed position" can be anywhere in principle. But not more than a few dozen miles for better practical results. There are reasons for selecting whole number latitudes and certain specific longitudes for the AP when using the popular sight reductions tables (tables "229" and "249" as they're numbered in the US series), but that's not really important --it's arithmetic to feed the tables what they require. A good and reasonable modern choice for an AP is just any convenient pair of "round numbers": like latitude +20.5° and longitude 32.0°W. This then implies that the center of the plot is a nice "round number" location, and the intercept distances will be effectively random numbers. They tell us where to plot the line of position for each sight, but the distance itself is usually arbitrary. So I repeat: ignore the intercept distances and just look at the triangle. If you don't have a guess based on that, no worries --more details coming!

Frank Reed