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    Re: Help - Unknown Compass Graduation Arrangement
    From: Nicol�s de Hilster
    Date: 2009 Oct 23, 08:31 +0200

    Frank Jones wrote:
    
    > An acquaintance recently acquired a Japanese manufactured compass with 
    > the customary 0-360 degree scale.  It apparently has a parallel scale 
    > that ranges from 0-64 and each 64th is further divided into five 
    > subdivisions.  Anyone have a clue what units are in use.  Although I've 
    > not personally seen the compass, the description provided seems to match 
    > some common pocket compasses.  Apparently it has a mirror and a sighting 
    > arrangement.  I think the only other information visible on the compass 
    > is in English and is something like "Engineer Compass'.
    >   
    The 0-64 division is most probably the 'mil' or 'mils' system. This 
    system originated from the army and originally divided a radion in 1000 
    parts. With a circle being 2 PI Radians a full circle would then have 
    6283.19 divisions which were rounded down to 6283. This being not the 
    most handy way to divide a circle caused a second system to appear that 
    had the circle divided in 6400 parts. So the compass described to you 
    has divisions for each 20 mils, while every 100 mils is annotated with 
    the-angle-divided-by-100.
    
    I found a description of a similar compass at Google books (being quite 
    long the link might appear broken in several parts, but it should be 
    pasted in one whole part into the url field of your browser): 
    
    http://books.google.nl/books?id=deRKF5kv5wwC&pg=PA511&lpg=PA511&dq=circle+divided+6400&source=bl&ots=EtooExcaVI&sig=AO6f7xoLVW1zAqugwn4mD-Axopw&hl=nl&ei=VUrhStG-A47d-QabvOnkAQ&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCcQ6AEwBw#v=onepage&q=circle%20divided%206400&f=false
    
    Wikipedia also provides some info: http://en.wikipedia.org/wiki/Angular_mil
    
    Nicol�s
    
    
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