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    Re: Bygrave slide rule
    From: Bruce Hamilton
    Date: 2008 Sep 27, 19:30 -0700

    Thank you for the post on the Bygrave Slide Rule.  It is a particular
    favorite of mine.  I actually used slide rules in hight school, and
    learning to use them was still taught as a part of math. I certainly
    learned how to estimate accurately!  We were the last class to do so.  I
    hope to put together a Bygrave as a winter project once the winter rains
    come and the sky turns grey for the next several months.
    Speaking of slide rules. (I love asking odd questions on this list as
    there are many minds whose mix of applied math and practical thinking
    can actually answer the questions that would keep me up all night.)
    Where else would I be able to confirm that celestial navigation on Mars
    would be not much different than here.
    Anyway, I was looking at almanac tables and wondering if, because of the
    regularity of the change, if they could be put on something like a
    bygrave slide rule, where you set the date and read off the GHA and the
    Dec.  I was thinking Bygrave as the scales are long enough to be very
    accurate. It would still be much bigger than 50 year tables that
    Geoffrey came up with. They saved my night the other night as I was
    sitting on a bench on the seawall here in Vancouver, practicing with my
    A12 when my Palm pilot died. The sudden lack of electronic almanac did
    not dampen the night's events as I then whipped out the 50 year almanac
    and read and penciled my way through the sites. It is much lighter than
    my Norie's that tends to become my desk.
    On the other end of the spectrum, I love the IKamal concept. Heck I
    would be happy with a sextant with optical rotary encoders linked to a
    BIG display. Watching me swap glasses and drag out a magnifier in order
    to read the vernier on my A-12 would make a good comedy skit.  I had a
    quick look at off the shelf digital levels, but was unable to find
    anything with an accuracy of greater than 0.1 degrees. I looked at some
    expensive tilt indicators and they were not much better.  I have read
    about modern self leveling theodolites, and suspect that they might have
    the needed technology, but have yet to find what mechanism they use to
    self level.  A separate digital camera looking at a horizon bubble could
    certainly work.  I imagine that a good digital camera linked to
    appropriate software will be the ultimate high tech "sextant", but I
    still like the idea of having something that works like a traditional
    sextant but is very high tech.
    Bruce Hamilton
    Vancouver, BC
    VE7 BRH
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