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    Re: Azimuth Equation revisited
    From: T. Shanklin
    Date: 2005 Oct 19, 22:32 -0700

    Well,
       After reading some of the replies I kept telling myself there is no way
    that I would have made such a mistake in my programming as simply forgetting
    a set of grouping parentheses- it had to be much worse, much more
    complicated than that... that whole parentheses bit was just a mistype on
    the email as it was late and I was tired.  I would never make such a silly
    mistake as if I were  a child back in pre-algebra, standing by my teacher's
    desk as he explained yet again why it is so important for me to get my
    parentheses straight.
       However- upon inspection just now after along day of work, I notice that
    INDEED, I had forgotten a set of parentheses and must attribute that to
    programming my calculator also after long days of work and being tired.  And
    upon correction, my problematic LHA values were no longer problematic.
    Huzzahs to you all for the help.
       But I am still wondering why the equation worked just fine for all the
    other values and only started giving me error messages after LHA>345
    degrees.  All my Zn calculations were fine until then.  That will give me
    something to do for the next couple of nights.  I've also tracked down the
    alternative azimuth equations in Bowditch for even more fulfilling evening
    pursuits.
       Further, while we are on the subject: What exactly is meant by Step 3 on
    pg 279 of the N.A.?  Is it simply that if the value calculated for X is
    greater than 1, then X is assigned the value +1, and hence when A is
    calculated (cos-1 X) it is simply 0 degrees True, and 180 degrees True if
    the value of X is less than -1 (hence = -1)? And what is defensive coding?
    Am I correct to assume simply putting in the If clause in my programming to
    insure that if X>+1, then set it equal to +1 &c.?
       Thank you all for your help, once again.  I do hope I am improving.  And
    for what it is worth, for the complete example set of values for the Altair
    sight I included in my original e-mail:
    LHA= 354.0575
    Dec=8.885
    Lat=38.563
    Hc=59.84507789
    Zn=168.2510887
    Hs=59 59.8 (59.99666667)
    DIP=-5.9' (-.0983333333)
    IE=-0.84' (-.014)
    Ha=59 53.06 (59.88433333)
    Ref=-0.6 (-.01)
    Ho=59 52.46 (59.87433333)
    Int=1.755' Towards (.0292554389)
    
    I have been recently shooting sights down to an intercept of .02'- quite
    thrilling.  Although I am shooting from the dry.
                                      Todd Shanklin
                                      Salt Point State Park
                                      N38 33.78  W123 20.35
    
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