NavList:

Last night I wrote: "Three nm accuracy is very good, and 20nm accuracy is not uncommon".    Upon review, perhaps ‘not unheard of’ might be a more accurate description than ‘not uncommon’.  I also wrote: "Therefore, Air Navigators are advised that if they have a choice, they should use the Q correction from the current Air Almanac".   So, when might you use the Q correction table in Vol1 rather than the Air Almanac Value?  Well, if you intended to use a Polaris LOP with one or two LOPs from Vol1 to produce a fix, and you intended applying a P&N correction to the final fix rather than to each assumed position, then if you’d used the current Air Almanac Q correction' you would have effectively applied P&N to the Polaris LOP twice.  However, I ought to add that although Polaris sounds a gift in terms of reduction, in my experience, it was rarely used in the air, unless there was nothing else available, because it’s relatively dim, and it doesn’t exactly jump out at you through the eyepiece of a periscopic sextant to give you that warm fuzzy feeling of recognition.  DaveP