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    Re: Instumental error?
    From: Bill B
    Date: 2005 Apr 20, 15:42 -0500

    Alex wrote
    > But when I made almost simultaneous shots of the same distance
    > with two sextants (The other was Bill's new Astra) and obtained
    > a correct result with the Astra, and +0.4 error with my sextant,
    > I finally concluded that there is arc error.
    Remember these comparisons were made near midnight after a sailing-club get
    together (and boring Power-Point presentation) and included playing with
    tripod mounting sextants, and viewing Jupiter's moons with your binoculars--
    at a picnic table with enough security lights around to blind an Indiana
    If I recall, the target separation was calculated at 51d 6.8'.  No
    adjustments required for abnormal refraction. (We did not adjust for
    sea-level barometric pressure corrected to 706.92736 ft above sea level ;-)
    The Astra consistently measure 51d 7.0 in your hands with my scope (IC -.5)
    so corrected to 51d 6.5' or -0.3' from target.   I cannot, repeat the -.3
    result.   Over 50 observations indicate -0.1' in the mid-fifties range for
    my Astra.)  I do not recall your averages for the SNO-T, but 0.4' sounds
    about right.

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