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    Re: Ageton method and HO 211?
    From: Paul Hirose
    Date: 2014 Sep 26, 09:47 -0700

    HO 211 is more complicated and there's greater chance of a blunder,
    compared to "inspection tables" such as HO 229 or 249. In the latter,
    altitude and azimuth angle are already computed. You only have to look
    them up. Of course the tradeoff is a much larger table.
    
    An advantage of HO 211 is that it's not necessary to use an assumed
    position (different for each body) in order to get integer latitudes and
    LHAs. You simply use your DR position. This partly compensates for the
    more laborious computation, and makes for a neater plot.
    
    A disadvantage is that the HO 211 loses accuracy when LHA is near 90 or
    270. In fact, exactly at those angles the solution is indeterminate.
    
    Several HO 211 "improvements" have been published. The length of the
    table can be cut in half by giving the A and B values for every whole
    minute instead of half minute. And by taking advantage of mathematical
    symmetry (e.g., A of 10° = B of 80°), it can be halved again.
    
    I've found the latter trick not worthwhile. It's harder to avoid
    mistakes, since the A function of an angle is not always in the left
    column, and the B values are not distinguished with boldface type. The
    redundancy in the original Ageton format doubles the page count, but
    twice a small number is still a small number.
    
    HO 211 is small enough that it's sometimes included in other works. My
    Bowditch Volume 2 (1981?) has it. So does the 1939 edition of "Practical
    Air Navigation" by the U.S. Coast & Geodetic Survey. A scan of that book
    is available from the successor agency (NOAA), under the alternate title
    "Special Publication No. 197". It's an interesting time capsule of air
    navigation techniques on the eve of WW2.
    
    http://www.lib.noaa.gov/collections/imgdocmaps/cgs_specpub.html
    

       
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