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    Re: Round-off
    From: John Karl
    Date: 2009 May 14, 19:17 -0700

    > Frank wrote:
    > That's right except for one little detail. Round-off error is a random 
    number taken from a uniform sample distribution. What you want for the step 
    size if not the maximum size of the round-off error, but the standard 
    deviation of that. You'll find that this amounts to 1/sqrt(12) times the 
    width of the round-off band. So if you have a dozen numbers added up where 
    you've dropped the tenths, your expected error is only ONE tenth.
    This question is more a matter of navigational philosophy.  I
    subscribe to the old adage that it's most important to know where you
    are not, i.e., DEFINITELY where you are not.  And that's not a matter
    of statistics.  I'm not satisfied to miss reefs only a percentage of
    the time.  So I look at the maximum round off error. Rounding every
    one of 12 numbers to the nearest whole minute could lead to a maximum
    error of about 0.4'x12 = 4.8'.  Why introduce this possible error when
    it's completely unnecessary?
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