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    Re: Navigation spreadsheet lessons
    From: Peter Fogg
    Date: 2009 Jan 17, 19:35 +1100


    Frank wrote:

    We need one more formula to get near the almanac table. Refraction modifies dip by some factor. So let's add a label below "R earth:". In cell A16, type "ref factor:". Then in cell B16, enter 0.85 ...

    And now we can finally do something useful with this spreadsheet. You can enter trial values for "ref factor" until your table matches the one in the Nautical Almanac. And just that easily you have reverse-engineered their table.
     

    The "ref factor" that gives the same results (to six or seven decimal places) as the formula:
    Dip = (sqrt height of eye in feet)*0.95
    is 0.8935097, but I guess that this formula uses an approximation of refraction anyway .. and maybe the 0.95 is also an approximation?

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