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    Re: Arg 1 Ww 11 U Boat Navigation Device Ebay Item Number: 370193239339
    From: Gary LaPook
    Date: 2009 May 23, 03:45 -0700

    In response to your request, I have attached the article on the ARG1 written 
    by David Charlwood in the Summer 2002 Navigator's Newsletter. Unfortunately 
    we were notified last summer that the Navigation Foundation was going to 
    close its doors since it remaining officer could no longer keep up the 
    publication.
    
    This entire article is contained in the attached ARG1-1 through ARG1-9 PDF pages.
    
    In the same issue there was a another article by Robert Girder describing a 
    Great Circle Slide Rule that just happens to use the same method as the ARG1. 
    I have included his article as -10 through -11. His diagram is the same 
    equatorial stereographic diagram as that used in the ARG1 but not to the same 
    precision, you do not need a microscope to read it. However, we can use this 
    diagram to make a demonstration model of the ARG1 so see how it works.
    
    I added some labeling of altitudes to the diagram as -12, cut it out, made a 
    hole in the center and mounted it on the center pin of my 2102-D Star Finder 
    base. I then took a clear sheet of plastic, punched a hole in it and mounted 
    it over the diagram and then used a scissors to cut off the excess material 
    around the edges. I then added an index mark, see -13.
    
    I then worked the same problem as described in the article, declination 8?51' 
    N, LHA 29? and latitude of 51?00'N. Since I did not have any microscopes to 
    set I simply set my index mark on the plastic sheet overlay to 90? and marked 
    on the sheet a dot to represent the declination and LHA, see -14. Obviously, 
    this visually interpolated dot cannot be nearly as accurate as the cross 
    hairs in the microscope of the ARG1. I then rotated the index to the 51? mark 
    which then brought the dot representing declination and LHA to the position 
    on the grid showing the Hc and Az. See -15. I read out an Hc of about 40? and 
    an azimuth of 220? (40 plus 180 since I did not re-label the azimuth scale on 
    the diagram to avoid clutter.) This is pretty close to the answer given in 
    the article of Hc 41?34' and Az of 220?.
    
    Hopes this helps.
    
    gl
    
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