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    Re: Sumner's Line (Navigation question)
    From: Henry Halboth
    Date: 2006 Feb 15, 13:26 -0500

    It is unnecessary to compute two positions to lay down a line of position
    by Sumner's method, albeit this is how it was originally discovered and
    done. The Latitude and Longitude ascertained by a single Time Sight
    computation, regardless of the Latitude employed, establishes a point on
    a line of position which is entirely accurate - a line drawn through that
    position at right angles to the computed azimuth of the body employed is
    the same LOP as determined by any other method, and just as accurate.
    Ulitmately this is how the Time Sight was employed in LOP navigation with
    very little difference in computational work/time than the intercept
    method employed by Marc St Hilaire. It was at one time the predominant
    method employed in the US Merchant Marine. You probably knew this, but
    based on previous postings it doesn't seem to have been dealt with.
    On Wed, 15 Feb 2006 01:24:58 -0800 "Gary J. LaPook" 
    > Capt. Sumner had to work the time sight twice, doing the math two
    > times
    > which was difficult in the days before inspection tables and
    > computers.
    > Marc De St. Hilaire's contribution was his method that allowed you
    > to
    > lay down Sumner's LOP while only doing one computation. Most still
    > cling
    > to this method today in spite of the development of compact
    > computers.
    > This still means you have to determine an AP, plot it on the chart,
    > measure the ZN and measure off the intercept.
    > A simpler method is to use Sumner's original system but with a
    > computer.
    > A long time ago I programed my handheld calculator to compute the
    > latitude of a LOP given a longitude or the longitude given a
    > latitude.
    > It automatically computed two such points, one east and one west of
    > the
    > dead reckoned position (or one north and one south) so all I had to
    > do
    > was plot these two points on the chart and draw a straight line
    > between
    > them with a straight edge, no measuring azimuth or intercept, an
    > easier
    > way to lay down the LOP and less chance for error. People should
    > consider using this new (old) method today.
    > Gary LaPook
    > >
    > >

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