# NavList:

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

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Re: errors in plotting and a possible/partial fix thereof, as menti...
From: Gary LaPook
Date: 2010 Dec 29, 11:14 -0800

Jeremy wrote:

"If I am using the GPS fix as the AP, I first have to advance and retard each of the stars along the track line. The trouble then becomes that I have such small intercepts it is difficult to mark them accurately (my normal dividers leave a 2mm gap between points). My other dividers have much larger points which are also not as accurate. Then I have to spin the triangles from the azimuth to the LOP angles and i always get a bit of error trying to get the exact distance from the AP. Do this over 5 stars and so, and the error just starts to compound."

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Jeremy, look at my prior posts on mathematically advancing LOPs. In addition to the tables I posted you can also use the Motion Of the Observer table in HO 249, just divide the speeds by one hundred and the corrections by one hundred. For eighteen knots just double the 9 (900) knot correction. The table I posted goes up to 15 knots but you can calculate the values for higher speeds and make you own table.
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http://www.fer3.com/arc/m2.aspx?i=114591&y=201012

15 knot table

http://fer3.com/arc/img/114591.moo-rev.pdf

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http://www.fer3.com/arc/m2.aspx?i=114523&y=201011
http://www.fer3.com/arc/m2.aspx?i=114867
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Five minute table for eighteen knots:

http://fer3.com/arc/img/114867.moo%2018-5.pdf
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http://fer3.com/arc/m2.aspx?y=200807&i=105937

http://fer3.com/arc/m2.aspx?i=111994

http://fer3.com/arc/img/111994.moo.pdf

http://www.fer3.com/arc/m2.aspx?i=114568&y=201011

gl
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