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    Re: slide rule sight reduction accuracy
    From: Gary LaPook
    Date: 2009 Jun 18, 03:04 -0700

    I have attached a revised form that carries the azimuth rules used with
    my version of the Bygrave. These are slightly different than the
    original rules with the original Bygrave due to my simplification of the
    scales. I omitted the second set of numbering on both scales, those
    running from 90 to 180, to keep the scales uncluttered. The results are
    the same as a value exceeding 90  will be found at exactly the same
    point on the scales using my method or using Bygrave's. For example, LHA
    150, Hour Angle (H) 150 west on the original Bygrave will be found at 30
    on my version, the same point that is also marked with "150" on the
    original Bygrave. The same thing happens for values on the cosine scale.
    
    The original Bygrave produced azimuths in the range of 0 to 180 and are
    always laid off from the opposite pole while with mine the azimuth is
    determined in the range of 0 to 90 and are laid off from either pole as
    determined by the rules on the form.
    
    Here is a link to my original post:
    
     http://www.fer3.com/arc/m2.aspx?i=107414&y=200902
    
    (Note I made an error in the explanation of the sample problem, the
    declination is 20 north not 14 north. I also used a form for the
    illustration using Byrave's "y" instead of my "W".)
    
    Due to my simplified scales I introduced on additional intermediate
    value "X" and, for clarity's sake, I replaced Bygrave's lower case "y"
    with "W". Then using "W" with "X" I derive a "Y" in restricted to the
    range of 0 to 90. Using my method computes the same values as when using
    the original Bygrave.
    
    Notice that "X" determines the final Zn. If "X" exceeds 90 then Zn is
    laid off from the nearer pole and from the far pole when "X" is less
    than 90.
    
    Here is a link to the Bygrave manual:
    
    http://www.fer3.com/arc/img/107419.bygrave-manual.pdf
    
    gl
    
    
    
    
    Paul Hirose wrote:
    > Regarding the Bygrave simulation, it can be done if I know the rules.
    > For instance, azimuth is obtained by taking an arctangent, but that
    > function yields a result between -90 and +90. There must be some rule to
    > convert that to the range 0 to 360.
    >
    >
    
    
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