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    Re: Calibrating a sextant scale
    From: Frank Reed
    Date: 2007 Nov 23, 00:24 -0500

    On collimating tables... Might as well go to the original. You can read all
    about one of the earliest in the Proceeding of the Royal Society from
    1867/68. Here's the first few lines of the article:
    "I. "Description of an Apparatus for the Verification of Sextants designed
    and constructed by Mr. T. Cooke, and recently erected at the Kew
    Observatory." By BALFOUR STEWART, LL.D., Superintendent of the Kew
    Observatory. Received May 9, 1867.
    In order to test the accuracy of graduation of a sextant, it is necessary to
    have a series of well-defined objects, the angular distances between which
    must be accurately known. The sextant under trial is made to measure these
    angular distances ; and the results thus obtained, when compared with the
    correct values of these distances (supposed to be otherwise determined),
    will give at once the error of the instrument. "
    Here's a link to the article on google books:
    I am attaching a diagram from the article. I've changed the the image in an
    effort to make it a little easier to figure out.
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