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    Calculators for Navigation
    From: Bill Murdoch
    Date: 1999 Mar 13, 7:01 PM

    In a message dated 3/12/99 7:47:41 AM EST, titom{at}ix.netcom.com writes:
    
    > What type of calculator is the best for working the calculations, should it
    > be programable?
    
    After you master the needed calculations and plotting by hand, Nautical
    Almanac, and sight reduction tables; I think you would be best off with a
    programmable calculator.  Calculators are (still) cheaper than computers and
    are much more rugged.  Much of my enjoyment of celestial navigation has come
    from programming programmable calculators for sight reduction.
    
    I started off with a HP-11C that had enough memory to hold the cosine sight
    reduction formulas and the other calculations that are detailed in the
    appendix of the Nautical Almanac.  That worked well enough, but I wanted to
    free myself from looking up the astronomical data in the almanac.  I wanted to
    calculate the data myself.
    
    From the British Library I got a copy of the booklet, B. Emerson, N.A.O.
    Technical Note Number 47 - Approximate Solar Coordinates.  The booklet had
    reasonably short 0.1' formulas for the GHA, declination, and semi diameter of
    the sun that are good for a couple of hundred years.  I used them to write a
    program for a TI-Galaxy 67 calculator that would produce an intercept and
    azimuth given the day, date and time, the D.R. latitude and longitude, the
    solar limb observed, the sextant altitude, the index correction, the height of
    eye, the temperature and the pressure.  I worked the program into a January
    1994 article for Practical Boat Owner, "A Sun Sight Calculator for �17".
    
    A year of two later I modified the program to run on a TI-81 calculator.  That
    program was published in Cruising World in March 1996.  I later rewrote it to
    run on a TI-82 or TI-83.
    
    The TI-82 had enough memory to do much more, so I expanded the program.  In
    that calculator program I included the moon, four planets and 92 stars.  I
    added the ability to reduce multiple sights to a lat/long fix, mercator
    sailing, great circle sailing, sunrise - sunset prediction, and a bunch of
    other things.  I was unable to find a publisher for the program (It is about
    200 pages typed.) and sold it for three years through a classified ad in Ocean
    Navigator.
    
    All of this has been great fun.  I have learned a lot, met quite a few
    interesting people, and filled more than a few quiet evenings.
    
    Bill Murdoch
    
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