NavList:

   

Reply

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


--~--~---------~--~----~------------~-------~--~----~
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply