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    Re: S-table and long term almanacs
    From: Hewitt Schlereth
    Date: 2015 Feb 9, 11:13 -0800
    Hanno hit on one of the things I find particularly annoying about the NA reduction tables - their lack of a diagram of the underlying spherical trig geometry and formulas.

    This method is one that divides the basic PZX triangle into two right spherical triangles. Other methods (Dreisonstok; Ageton) that do this have labeled diagrams and show the formulas that solve for the arcs and angles of the right triangles involved.

    Admiral Thomas D. Davies' 1984 version of what became these NA SR tables - Concise Tables for Sight Reduction - does have a diagram, but does not show the formulas.

    Hewitt

    On Feb 9, 2015, at 10:21 AM, Hanno Ix <NoReply_HannoIx@fer3.com> wrote:

    Geoffrey,

    reading this with interest.

    The  widespread use of the NA tables is not a significant assessment of their actual quality or practicality.

    To be a little cynical for a moment: There was once a method of transportation - widely accepted and used : buggies and horses. Why, then, would one have entered the rarefied halls of engineering and thermodynamics to create an automobile?

    I sense there are some extraneous reasons for the use of those tables: they may be the favorite method of a prominent club or training center, maybe because of some didactic concern or the availability of study material.

    Even if the NA tables are widely accepted and used I don't think they are widely understood. I cannot find much detail but they appear to be an attempt to simplify sight reduction by publishing a list of pre-calculated spherical triangles and a method to interpolate/extrapolate linearly to the actual situation. The idea seems sound, the execution less so: if you use the published work forms, for instance, you will find yourself quickly in a mess of  tables, additions and subtractions with numerous opportunities to blunder and no means to check your work. Compare this with G. Rudzinski's index card approach!

    To properly assess the merits of the NA approach I need to be able to compare it with the strict formulas for Hc and Z, and to estimate residual errors and their dependency on L, d, and LHA. I have yet to find a  clear description of the geometrical considerations, the assumptions made and the approximations chosen for the NA approach. I would be oblidged if you could hint where to find such material.

    So far I have seen only these tables and work forms, and so  far I am not impressed.

    Regards

    H






    On Sat, Oct 4, 2014 at 8:56 AM, Stan K <NoReply_StanK@fer3.com> wrote:
    The NA tables are currently the only tabular method taught as part of the United States Power Squadrons courses, on the theory that they are contained in a book you require anyway.  They have taught other tabular methods in the past, and still publish a Sight Reduction Methods "learning guide", which includes compact HO 211 (Ageton-Bayless), HO 229, and HO 249.


    -----Original Message-----
    From: Geoffrey Kolbe <NoReply_GeoffreyKolbe@fer3.com>
    To: slk1000 <slk1000---.com>
    Sent: Sat, Oct 4, 2014 3:57 am
    Subject: [NavList] Re: S-table and long term almanacs




    On Fri, Oct 3, 2014 at 6:05 PM, Carl Roberts <NoReply_Roberts@fer3.com> wrote:

    maybe dr Kolb could boot the NA reduction and include Alan Bayless or S-Table.
    ​There is a perception that "nobody uses the NA tables" and so they should be replaced by something else. However, my feeling is that outside the rarefied ​halls of this list's discussions, the NA tables are widely accepted - and used!

    Geoffrey Kolbe


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