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    Re: Formulas to Compute LHA
    From: Lu Abel
    Date: 2009 Jun 28, 09:04 -0700

    Hmm, never thought of NP vs SP "up" in a time diagram, but I realize the
    time diagrams I am used to using are NP up.
    Problem with NP up is that angles go in the "wrong" direction.   From
    everything from high school math to compass roses, we are used to angles
    increasing clockwise.   But in a NP up time diagram angles increase
    CCW.    Looks like SP up is/was an attempt to "correct" that.   Sort of
    like the US Navy correcting Benjamin Franklin's error in saying that
    electrical current flows from positive to negative; my dad served time
    in the US Navy as an electrician and all his textbooks had current
    flowing from negative to positive (and right-hand rules being replaced
    with left-hand rules).   Fun reading years ago for a nascent electrical
    engineer (yours truly).
    For what it's worth, Bowditch uses a NP up time diagram (see Fig 1525b
    in Chapt 15)
    Lu Abel
    waldendand{at}YAHOO.COM wrote:
    > I find it necessary to be very cautious reading "time diagrams".  Very 
    reputable sources find themselves "poles apart" on the NP up vs SP up issue.  
    (Why is this?)
    > >
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