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    Re: Cryptic Slide Rule Formulae
    From: Greg Rudzinski
    Date: 2016 Jan 21, 06:16 -0800


    (6.) is the prime vertical formula used with the azimuth formula (2.) when the azimuth is near 90° or 270°.

    (7.) is the amplitude formula used to determine the azimuth of the Sun when the lower limb is 2/3 of a diameter above the visible horizon.

    Greg Rudzinski

    From: Jim Rives
    Date: 2016 Jan 20, 12:58 -0800


    My father-in-law, who sailed for years out of Huntington, LI, passed away a year ago.  In one of his desk drawers I found a 10" Sterlin Slide Rule, No. 584.  It is white plastic, not very eleborate.  (however, still beyond my slide rule skills!)  He had scratched the following 7 formulae on it.  I am just wondering if anyone would recognize the text or method he was using this rule for:  

    In no particular order:  

    1.     sin h = sin L sin d + cos L x cos d cos t

    2.     sin z = cos d sin t sec h

    3.     cos co-d = cos co-h cos co-L + sin co-h sin co-L cos z

    4.    sin t = (sin z sin co-h)/sin co-d

    5.    cos t = tan d cot L

    6.    sin h = sin d csc L

    7     sin A = sin d sec L 

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