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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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