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    Re: Exercise #16 High Altitude Sights near Noon
    From: George Huxtable
    Date: 2008 Jul 21, 23:13 +0100

    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.
    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.
    Navigation List archive: www.fer3.com/arc
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