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    Re: Bygrave position line slide rule
    From: Dan Allen
    Date: 2004 Feb 28, 20:48 -0800

    Zvi Doron wrote on Saturday, February 28, 2004 8:02 AM:
    Henry Hughes & Son of London, England used to make a cylindrical 3 part
    position line slide rule for astro navigationsometims called "Bygrave" that
    worked on the principal of solving two right angle triangels instea of the
    complete PZX in one calculation. Francis Chichester used one on his epic
    solo flight across the Tasman Sea (1931) and Weems in his book "Air
    Navigation - British Empire Edition" gives a drawing and a few details. I
    could not find any reference to it on the web.
    Has anyone - ever used one? got one? seen one? knows if they can be had and
    for how much? Any information will be gratefuly received.
    I found one thing from Google:
    The Otis King Slide Rule
    This slide rule consists of a body with a helical scale, on which a sleeve
    with a similar helical scale could both slide and rotate. An outer sleeve
    then slid and rotated on that sleeve at one end, and at the other end was
    constricted to slide directly on the body. Marks at the two ends of that
    sleeve constituted the cursor of the slide rule; thus, instead of placing
    the two helical scales in coincidence, points on the two scales separated by
    the distance between the two cursor marks were treated as corresponding.
    The Otis King cylindrical slide rule was perhaps the most popular and
    inexpensive circular slide rule made.
    A special-purpose cylindrical slide rule made for use in sight reduction for
    celestial navigation, the Bygrave position-line slide rule, was based on the
    same principle.
    As a mathematician, I simply turned your problem into a different one: what
    the heck is an Otis King slide rule?  Sounds very interesting!

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