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One slight caveat I have with sight reduction tables - such as the
NAO tables in the Nautical Almanac - which use an "assumed position"
(by which I mean an initial position chosen for the convenience of
the tables) is that the assumed position could well be half a degree
away from your DR position let alone your "true" position. That being
the case, I did some sums a while ago to see what sort of errors
would result from the fact that the LOP is in fact a circle and not a
straight line. From memory,  I found for altitudes of around 50
degrees, errors of around 0.5 NM could result. This is within the
expected accuracy of one minute for the NAO tables, but non-the-less
represents a significant error which cannot be reduced by iteration
in the same way that you could in principle with tables like
Ageton's, which use the DR position as an initial position.

Geoffrey Kolbe

   

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