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    Re: Centring Error Detector
    From: George Huxtable
    Date: 2007 Jan 13, 20:46 -0000

    Phil wrote-
    | Here is another model of "calibrator", more recent manufacture :
    | http://www.hiboox.com/image.php?img=8eb1dd05.jpg
    | I do not have any information on this instrument. Does anybody knows
    I can try a guess.
    There seem to be three collimators; going clockwise, in order, call
    them A,B,C.
    In this context a collimator is likely nothing more than a
    straight-filament lamp, at the focal point of a lens, the whole
    assembly rigidly assembled in a way that allows precise positioning.
    It produces a broadish beam of parallel light, in a very well-defined
    The sextant is placed, side on, with its index arm pivot aligned
    roughly (no call for great precision here, as I see it) with the cenre
    of the sweep-arc of  movable collimator C. A shines into the horizon
    mirror. B, exactly parallel with A, and looking into the same point as
    the centre of arc C, provides the index error.
    And then you just swing C around to whatever scale angle you like, and
    take the reading of the sextant when the two bright lines,
    corresponding to A and C, align.
    Of course, the whole thing depends crucially on exact caliration of
    the arc that C is mounted on. How that calibration is obtained, I have
    no idea.
    The other thing that puzzles me a bit is why B is necessary. Why
    couldn't that angle, at zero degrees, be catered for by just swinging
    C into the position that B occupies? Any ideas? Anyone understand it
    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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