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    Re: Sight Reduction via Daily Pages in NA v.NA Concise Sight Reduction Tables
    From: Geoffrey Kolbe
    Date: 2011 Jan 09, 06:19 +0000

    Alan wrote:
    Lately, I have begun to delve into use of the NA Concise Tables, a Power Squadron Nav course I'm taking requires reduction of sextant sights by both methods. I understand that the Concise Tables Method are supposedly simpler, easier to use.

    Perhaps they are, doing the Law of Cosines absent a calculator, using log tables would be tedious as hell, however as to the Concise Tables being "simpler/easier to use", I beg to differ, for it seems that the Concise Tables involve endless messing about with and or the massaging of numbers, which one doesn't have to do using the Law of Cosines. Of course, I might be missing a salient point perhaps more than one here, for instance what happens if one's calculator craps out. Of course, with the Concise Tables, one would be out of luck if they lost their NA over the side. Seriously though, is there something basic or obvious here that escapes me?

    In appreciation of any input or clarification offered.


    I agree with your sentiments entirely. The main problem is that the explanation in the NA for use of the NAO sight reduction tables is simply awful - or at least it was the last time I looked at a copy of the NA, which is some years ago now. For the second edition of my Long Term Almanac, I was persuaded by the publisher (Starpath Publications) to use the NAO tables instead of a version of Ageton's tables which I had used in the first edition, mainly because that is what is taught in most navigation classes.

    My only beef with the NAO tables is that you have to use an assumed position. But in their favour, it is angles all the way down - no lists of logs to add up or subtract.

    I spent quite a bit of effort in my LTA trying to make the rules of engagement for the using the NAO tables easier to understand. However, using the NAO tables is easy and quick provided you use a workform. A lot of time and effort by the good people at Starpath went into the design of the Starpath workform and that is what I would very strongly recommend you use. The form is in my LTA, but I think it can be downloaded from their website.

    Using a workform, a sight reduction using the NAO tables takes about two minutes - no more. I don't think you could do it quicker on a calculator.

    I have put the page from the LTA with the Starpath form here www.pisces-press.com/images/NAO_workform.pdf which should be OK, and it includes a short set of rules.

    Geoffrey Kolbe
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