NavList:

A couple of weeks ago, Paul Hirose pointed out that the directions for index correction in the N.A. "sight reduction procedures" have a slight flaw. The directions, present in this form for decades, say that we should add the index correction, and there's an explicit 'plus' sign in the directions. But this (slightly, technically) contradicts the usual sign choice for index error and index correction. It really should say something like "apply" the index correction, leaving the sign up the smarts of the navigator.

There's another little (slight, technical) issue that I noticed this morning. The equation for the SD of the Moon reads SD = 0°.2724HP as if it's saying that we multiply the HP by an angle equal to 0.2724°. But that factor is not an angle. As the instructions note the HP should be expressed in degrees, meaning we take the listed HP in minutes of arc and then divide that by 60 (assuming --not necessarily the case-- that we want the SD in degrees rather than minutes of arc) before we multiply it by 0.2724. This latter factor is not an angle. It's just the ratio of the Moon's radius to the Earth's radius. The average (in some sense) size of the Moon compared to the size of the Earth is 27.24% or 0.2724. There shouldn't be a degree sign in there.

Important note here: I am not suggesting that this is some awful error that needs to be fixed. It's a minor, tiny thing. But this is the sort of thing that some navigation students will stumble over. They'll look at this and wonder where this angle of 0.2724° has come from, but it's just a numerical factor. I bring this up only in case you (any of you out there) encounter a fellow navigator who seems confused by it.

Frank Reed