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    Re: slide rule sight reduction accuracy
    From: Gary LaPook
    Date: 2009 Jun 19, 03:50 -0700
    Here is the form I had meant to send. This uses my notation of "W" instead of Bygrave's "y" on the previous form.


    Gary LaPook wrote:

    Here is  the promised revised form.


    Gary LaPook wrote:
    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:
    (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:
    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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