# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Poor St. Hilaire
From: Gary LaPook
Date: 2007 Oct 29, 01:19 -0700

```Gary LaPook writes:

I learned something new in this discussion.  I had never heard that the
Sumner method had evolved into using just one point and an azimuth to
plot the "tangent" method. It may have been easier computationally after
azimuth tables were available but I think that plotting two points on a
chart and connecting them with a straight line is easier and less prone
to error and inaccuracy than plotting an azimuth. This is especially
true since you can choose the latitudes that are lines already printed
on the chart with tick marks showing the longitudes. By the time you
walk a parallel rule across the chart from a rose you are bound to lose
some accuracy. This is also a problem with the St. Hilaire method so the
original Sumner "chord" method would appear to allow the most accurate
plotting of the LOP and a calculator today makes fast work of the
computation.

gl

frankreed{at}HistoricalAtlas.net wrote:

>Gary, you wrote:
>"Today, with programmable calculators, it is trivial to go back to
>Sumner's method and plot the LOP after determining two points using
>the "time sight" computation."
>
>Right. And one advantage of the Sumner approach compared to the St. Hilaire
>intercept approach is that you can use any old graph paper, including graph
>paper drawn up on the spot. With a Sumner line, it doesn't matter if you
>have the correct local scale for minutes of longitude. Sumner himself erred
>by suggesting that his lines should be drawn on a Mercator projection, and I
>suspect it slowed the adoption of the method.
>
> -FER
>
>>
>
>
>

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