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    Re: sight reduction tables
    From: Lu Abel
    Date: 2007 Sep 29, 20:37 -0700

    Peter Fogg wrote:
    > George proposes:
    >     And yet there's a bit of a contradiction here, it seems to me, in the
    >     attitude of many small-boat navigators; those who prize their expensive
    >     sextants, reading to 0.1 arc-minutes, and wouldn't be seen dead using a
    >     plastic sextant, no matter how good it may happen to be. I raise
    >     this matter
    >     at the risk of reopening old wounds here, but it would seem to me
    >     that if
    >     HO249 is acceptably accurate, then so too would be a decent plastic
    >     sextant.
    >     I'm not arguing against Gary here; I simply don't know whether he is a
    >     member of the diehard posh-sextant brigade or not. But they exist,
    >     and for
    >     them, would the 1-minute precision of HO249 be considered good enough?
    > I suspect that the issues are not so simply comparable, George. One of
    > the problems with plastic sextants is their unreliability, rather than
    > lack of precision.
    Do you have any specific data to back up this assertion?  I'm not
    talking about the really cheap plastic sextants like the Davis Mk 3 and
    the European-made equivalent whose name escapes me at the moment, but
    rather the Davis Mk 15 and 25.
    These not only seem like well-made units, but for the cost of even an
    Astra, one could buy three Mk 15s.  One to fail, one to drop overboard,
    and one you can still use to navigate!
    I have to agree with George on the accuracy issue -- it's damn hard to
    get even 1' accuracy on a pitching, rolling small craft.   It's also my
    understanding (at least as of a decade ago or so) that most of the long
    distance voyagers that still practicing celestial navigation use Ho249,
    since it's smaller and much easier to use, even if giving only 1' of
    Lu Abel
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