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    Re: Sun, distances and self-confidence
    From: Frank Reed CT
    Date: 2005 Jun 11, 03:11 EDT

    Fred you wrote:
    "Does anybody have any  suggestions for measuring shade error?"
    Do an index correction using the  Full Moon bringing the Moon's direct limb
    into contact with the limb in the  reflected image (you could also use the
    bright, shimmering horizon directly  under the Sun --over water, that is). Then
    swing in each shade individually, one  shade at a time, without touching the
    micrometer. If there's significant shade  error, you will see it right away as a
    gap or overlap that was not there  previously. Adjust the micrometer until
    that difference disappears and record  the change. Shade errors, of course, add
    linearly so if you know that shades A,  B, and C have separate errors of +0.5,
    +0.7, and -1.0 minutes of arc then using  all three together, e.g. for a Sun
    sight, would yield a net shade error of +0.2  minutes of arc.
    42.0N 87.7W, or 41.4N  72.1W.

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