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Hewitt Schlereth wrote-

"I've long been curious to discover just how close one could come with
the super-basic method of advancing arcs or circles position at the
standard Universal Plotting Sheet scale, which is why I was glad to be
presented with Jeremy's example from a CG exam."

As long as a position circle is a small one, the sort of circle you might
draw on a plotting sheet, then advancing circles of position is indeed a
perfectly valid method of proceeding. And that was particularly true for the
very high-altitude example quoted by Jeremy, and referred to by Hewitt..

But a word of caution is called for in advancing position circles, in the
general case, if these are the large-radius circles that you get when
observing a body far from the zenith. Then, advancing a position circle (by
a known course and distance) can result in a somewhat eggy shape on a globe,
that's no longer a circle at all. I'm sure Hewitt is aware of this, but many
navigators get it wrong. It's valid to advance just the relevant part of the
arc by the right amount, to find an intersection, but advancing the whole
circle becomes a contradiction.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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