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    Re: Northing correction to Noon longitudes.
    From: Bill Noyce
    Date: 2005 Jun 7, 12:18 -0400

    Frank's method requires adjusting each sight for the combined
    motion of the vessel and sun toward or away from each other on
    a north/south line.  He described it as moving the points before
    noon one way, and the points after noon the opposite way.
    George asked how "noon" is identified, since that's one of the
    unknowns we're looking for.
    As far as latitude is concerned, this procedure is no different
    from the normal procedure of "advancing all sights to a common
    time", so the resulting latitude is the vessel's latitude at the
    time chosen for the zero adjustment (which is probably not local
    noon).  I hope this much is obvious.  Note that the declination
    to be used in computing latitude is the one for the chosen zero
    time, not the one where the highest (adjusted) altitude was plotted.
    The longitude that results from the paper-folding exercise is the
    vessel's longitude when it and the sun were on the same meridian
    (i.e., when local noon occurred at the vessel).  If you're traveling
    mostly east or west, you could assume the latitude measurement is
    also valid for this moment.  Conversely if you're traveling mostly
    north or south, you could consider this longitude to be valid for
    the moment at which you measured your latitude.  If you're only
    moving a mile or two every 10 minutes, you could choose to ignore
    the difference.  Or you could advance or retard the longitude or
    latitude measurement to the time of the other one.
    It's unfortunate (for us pedants) that the the two results don't
    naturally correspond to the same time...
            -- Bill

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