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    Re: Round-off
    From: John Karl
    Date: 2009 May 16, 06:29 -0700

    Peter, I repeat:  I am NOT talking about observation error from
    rolling decks, systematic error, plotting error, or anything else.
    I'm ONLY addressing round off error in the calculation of a sight
    reduction -- a St. Hilaire reduction.  I count 10 numbers used in such
    a reduction.  If every number is off by 0.05' in the unfavorable
    direction, the result is 0.5' in error due to round off.
    This 0.5' is the MAXIUM possible error.  It's not a statistical
    measure (such as an average error, probable error, max entropy
    estimate) from a uniform distribution of the 0.05' uncertainties in
    the numbers.  Of course, using 1.0' precision in the same calculation,
    such as W.F. Buckley does, gives a Max error of 10'.  As I mentioned
    earlier, the other calculation uncertainties arise from the Almanac
    data, and reduction tables if they are used.
    An appreciation of this calculation max error is important in several
    cases.  One is when you want to evaluate Cnav accuracy by comparing
    with a very accurately know position.  Then it's necessary to minimize
    the calculation error so that the remaining error can be attributed to
    observing skill, plus all the other factors you mentioned.  In the 1'
    Buckley calculation, frequently these aren't sufficiently separated to
    allow a conclusion.
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