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    Latitude and Longitude by "noon sight"
    From: Henry Halboth
    Date: 2005 Jun 9, 11:09 -0400

    Most recent posts on this List have dealt with the time sight for
    Longitude and the meridian altitude for Latitude as separate entities,
    without consideration as to how they were, in practice, combined to
    obtain the noon position, actually a running fix, by simple calculation,
    and without the necessity for plotting. From a historical perspective,
    there are several methods for accomplishing this end, however, the
    following working, in my opinion, is the simplest to comprehend.
    
    1. Observe for AM Longitude, intending time sight solution, and
    precalculate all elements other than Latitude. Hold completion of
    solution until LAN.
    
    2. Maintain as accurate as possible DR from time of AM sight to LAN, and
    by traverse table or computer take out difference of Latitude + departure
    for course and distance made good over time period. From departure
    calculate difference of Longitude (DLo) over time period.
    
    3. At LAN observe for Latitude by meridian altitude or, if necessary,
    reduction to meridian. Apply previously calculated difference of Latitude
    to obtain most correct Latitude at time of AM sight for Longitude.
    
    4. Complete working up AM time sight, utilizing Latitude run back from
    LAN, and obtain AM Longitude.
    
    5. Apply DLo to LAN, as calculated under 2 above, to AM Longitude - and,
    presto, position at LAN by running fix - no different than advancing
    LOP's over several hours.
    
    This is the way it was done by some well into the 1930's. There are other
    ways, including the Longitude Factor method per Bodwitch, but that given
    here is probably the easiest to understand. Actually it takes less time
    to do than to write about.
    
    Henry
    
    
    

       
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