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    The Noon Fix
    From: John Karl
    Date: 2009 Apr 12, 08:10 -0700

    Jim, now I'm a believer.
    I've taken the exact data from my previous post and applied your correction ( 
    Hstationary = Hmoving + Sn*T) to bring the H-Time plot from a moving vessel 
    (at 10 knts northerly) to what would be observed by a stationary observer.  
    The result is excellent, with the max error from the exact value generally 
    less that 0.1'.  I had to prove for myself (and hopefully for others) that 
    your simple linear approximation is valid for the highly nonlinear Sin(H) 
    altitude equation.  That was far from obvious to me.  Congratulations on your 
    George, I don't understand your point.  The curves of my previous plot are 
    data that would be observed from separate vessels traveling north at speeds 
    from zero to 10 knts.  All five vessels are at the same latitude (N69) at T = 
    0.  The plotted times are thus relative to this T=0 time and therefore show 
    the relative time shifts of LAN from the five different ships, this is what 
    we're discussing -- it's just what we want.
    BTW, I made no correction for changing declination for two reasons.  The max 
    rate 1'/hour is small, plus the altitude equation is symmetric in Dec and Lat 
    so the effect is the same for each (as Jim has in his discussion).
    Sorry for starting a new "thread" (as I think it's called).  But I can't 
    figure out how to make an attachment directly at the NavList site.
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