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    Re: Traditional navigation by slide rule
    From: Paul Hirose
    Date: 2016 Nov 12, 21:55 -0800

    On 2016-11-10 13:33, Bob Goethe wrote:
    > Attached File: http://fer3.com/arc/imgx/_Mark-2-Slide-Rule-User-Manual.pdf
    
    On the Bygrave form on page 7 I find the format of the formulas
    unnatural, though their meaning is perfectly clear. Isn't it usual for a
    variable which receives a value to be on the left? E.g., x=2 not 2=x.
    That's the way it works in all programming languages I've seen. But on
    the Bygrave form the assignment goes from left to right.
    
    On the same page, there's a problem with the rule that determines
    whether azimuth angle is measured from the north or south. Occasionally
    it's wrong, or maybe I don't understand it. Below are three examples. In
    each case Z itself is correct, but since declination is south of the
    latitude (but both are north of the equator), I put a "south" prefix on
    Z. That results in a wrong azimuth.
    
    LHA = 84
    H = 84
    L = 30
    d = 29
    W = arctan(tan d / cos H) = 79.3
    X = 90 - L + W = 139.2
    Y = 180 - X = 40.7
    Z = arctan(cos W / cos Y * tan H) = S 66.7 W
    Hc = arctan(cos Z * tan Y) = 18.8
    Correct Z = N 66.7 W, Hc = 18.8.
    
    LHA = 307
    H = 53
    L = 45
    d = 41
    W = arctan(tan d / cos H) = 55.3
    X = 90 - L + W = 100.3
    Y = 180 - X = 79.7
    Z = arctan(cos W / cos Y * tan H) = S 76.7 E
    Hc = arctan(cos Z * tan Y) = 51.7
    Correct Z = N 76.7 E, Hc = 51.7.
    
    LHA = 286
    H = 74
    L = 41
    d = 30
    W = arctan(tan d / cos H) = 64.5
    X = 90 - L + W = 113.5
    Y = 180 - X = 66.5
    Z = arctan(cos W / cos Y * tan H) = S 75.1 E
    Zn = 104.9
    Hc = arctan(cos Z * tan Y) = 30.5
    Correct Z = N 75.1 E, Hc = 30.5.
    

       
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