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    Re: dip, dip short, distance off with buildings, etc.
    From: Frank Reed CT
    Date: 2006 Jan 11, 06:44 EST

    Bill, you wrote:
    "To follow up on your use of  a 0.15 constant (R/(1-.15) for
    calculating dip, short dip etc., one might  question the entire system. "
    
    You bet. The entire system depends on a  very specific choice for the value
    of terrestrial refraction. Don't get me  wrong, the choice in Bowditch is
    certainly a good one "on average" --if you have  to pick one value, you couldn't do
    much worse. But how much should a navigator  trust those tables? This is the
    really interesting matter. If I look up a dip  short value, or if I estimate a
    distance from Table XV, what kind of confidence  can I have in the results?
    That "on average" choice in Bowditch could be very  wrong in fairly common
    atmospheric conditions. There are coastal locations where  significant temperature
    inversions occur each and every day, and these  definitely have a big impact
    on the numbers in the tables.
    
    -FER
    42.0N  87.7W, or 41.4N 72.1W.
    www.HistoricalAtlas.com/lunars
    
    
    

       
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