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    Re: AP terminology, WAS: 2-Body Fix -- take three
    From: John Karl
    Date: 2009 Nov 13, 12:33 -0800

    No one has addressed my question of why the St Hilaire method
    calculates an altitude at a location our ship is NOT at, when we've
    just measured the altitude where our ship IS at.  (For politically
    correct reasons, I'm not using the name of this location.)
    
    Now lets go back to Sumner's 1837 calculation, where he picked three
    different longitudes and calculated three points on the circular LOP.
    This calculation is exact, and the equation for each point is the same
    as the one of the two necessary in the St Hilaire method (thus each
    Sumner point is half the work of a St Hilaire reduction).  And he
    could calculate as many exact points as he wished.
    
    So I'll put my question yet another way:  Why is the St Hilaire method
    superior to Sumner's and consequently the only one used today??
    
    I claim that the answer to this question has been made confusing
    because of the conventional name (names?) used for the location of the
    St Hilaire altitude calculation.  As evidence of this confusion I note
    that some authors write that we need to assume some point because the
    distance between the GP and the LOP is too great to plot, that there's
    insufficient information to plot the LOP, or that iterations are
    required to get exact points on the LOP.  The Sumner calculation
    demonstrates that none of this is correct.
    
    JK
    
    
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