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    Re: Testing Scopes
    From: Bill B
    Date: 2006 Apr 20, 00:06 -0500

    Alex
    
    Thank you for a thorough look at the scopes.
    
    > Remarks. Observations with |4SD-true.4SD|>.4 are discarded
    > as SNO-T manual recommends.
    
    As you know, I have some problems with 4SD comparisons where SD is taken
    literally from the almanac.  Discarding observations where |4SD-true.4SD|>.4
    has to take into account mental interpolation of the almanac SD to be
    workable IMHO.
    
    For example:
    
    Date              SD     4SD
    
    March 28 2006     16.1   64.4
    March 29 2006     16.0   64.0
    April 21 2006     16.0   64.0
    April 22 2006     15.9   63.6
    
    A change of nominally 0.005' in reality can cause a change of 0.1' SD in the
    almanac. If identically observations are taken a day apart near a rounding
    up or down, one might pass the test and the other not.  If we interpolate
    around March 28/29 we have a more realistic 4SD of 64.2 to compare our
    observations against.
    
    In the worst-case scenario using the|4SD-true.4SD|>.4 rule around March
    28/29, +/- 0.2' error is already introduced into 4SD if using the almanac
    figures directly.  That leaves 0.2' operator and sextant error for two
    tangency observations, or < 0.1' error per tangency.  That's a tough mark to
    hit, and otherwise usable observations might be discarded (false negative).
    
    On the flip side of the coin--if it works the other way, some very sloppy
    observations might pass the test resulting in a false positive.
    
    Bill
    
    
    

       
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