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    Re: Sight Reduction via Daily Pages in NA v.NA Concise Sight Reduction Tables
    From: Gary LaPook
    Date: 2011 Jan 9, 01:17 -0800
    Here is my evaluation of several methods of sight reduction.
    I learned celestial from Mixter, fourth edition, and this book included 
    a complete reprint of H.O. 211 so this is the first sight reduction
    method that I learned. I soon bought a set of H.O. 214 and never looked
    back, H.O. 211 is my least favorite method of sight reduction. Of the
    _tabular_ methods I much prefer Dreisonstok at this point. (But I am
    real partial to my Bygrave slide rule.) When my eyes were younger I
    preferred the Weems Line Of Position Book but I have greater difficulty
    now using the Rust diagram. Apparently others complained about this
    because Weems includes a mathematical solution for azimuth in addition
    to the Rust diagram in the 1944 edition of his book. He made some other
    changes at the same time. He changed the arrangement of
    table A so now
    each page is entered by latitude not by LHA which adds convenience for
    working a number of sights from the same assumed latitude similar to the
    convenience of H.O. 249, H.O. 218 and of H.O. 214 compared to the
    _inconvenience_ of H.O. 229 (I still don't know why they changed the
    arrangement and ruined a good thing!) He also changed the size of the
    book from a handy 10 by 6 inches to a much larger 14 by 8 1/2 inches,
    not so handy but it does make the printing larger.

    So comparing the various standard methods of paper based sight reduction
    the Haversine- Cosine method takes the most work. The Sine -cosine
    method is a little bit less work but there is the problem with logs of
    negative values of cosine for LHA. Although this method can work with
    some cases, since it cannot be used in all cases it just makes a
    navigator's life more difficult to learn both of these methods. (It is

    probably the best method to use with a calculator, however.)

    I am attaching a list of keystrokes to use in solving this
     with a calculator. (Note, this corrects a typo in my original
    posting of the keystrokes so the previous version should not
    be used.)

    All the short tabular methods are more convenient than the previous
    two.Of the short methods H.O. 211 takes the most work (although it does
    allow working from the D.R. but this normally doesn't make any
    difference in practical navigation) followed by H.O 208 and the shortest
    solution is the Weems Line Of Position Book.

    The inspection tables, H.O 214, H.O. 218, and H.O. 249 have the same
    arrangement of tables and are equally convenient. H.O. 249 volume 1 is
    especially good when working a round of star sights as you don't need to
    compute individual LHAs so for this use it is better than the other
    tables. H.O 214 includes the necessary factors to allow working from a
    D.R. but you can also calculate these factors for H.O. 218 and H.O 249
    if you need to do this, such as for practice sights from a known
    location. These tables are only
    slightly faster than the Weems book. All
    the inspection tables take up more space on the shelf than the short tables.

    H.O 229 is not as convenient as the other inspection tables and requires
    more interpolations. However these tables might provide slightly
    greater accuracy for high altitude sights but this probably makes no
    difference for practical

    These are links to examples of sight reduction using different methods
    using data provided by Chichester all from the archives for December 2008.



    --- On Sat, 1/8/11, Alan <alan202@verizon.net> wrote:

    From: Alan <alan202@verizon.net>
    Subject: [NavList] Sight Reduction via Daily Pages in NA v.NA Concise Sight Reduction Tables
    To: NavList@fer3.com
    Date: Saturday, January 8, 2011, 9:11 PM

    Given that my efforts at Celestial Navigation are limited to, and unlikely to progress beyond standing on the beach, when I can get there, shooting whatever happens to be in view, day time and or evenings, it doesn't make a whole lot of difference, however I learned to do sight reduction using the NA Daily Pages and the Law of Cosines, which strike me as a simple to use, direct, straight forward approach to sight reduction.

    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.


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