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    Re: The mil as a unit of angle.
    From: Trevor Kenchington
    Date: 2003 Mar 11, 22:39 -0400

    Following on from Brooke and Marvin's contributions, the underlying
    point here is the basic bit of high-school math:
    Tan(A) = A  (as a very close approximation) ...  provided that A is
    measured in radians and provided that it is small.
    Hence Brooke's
    > In military artillery one mil is equivalent to 1 yard offset at 1,000 yards range.
    (incorporating his correction) makes the artillery mil essentially the
    same as Marvin's definition of the mil as a milliradian.
    The U.S. military decision to approximate the mil as 1/6400 of a circle
    and the Russian use of 1/6000 (as explained in the Web page cited by
    Marvin) are also understandable in the same terms: The numerical
    equality between angles in milliradians and corresponding linear offsets
    at specified ranges only works for small angles of arc. If you never
    measure more than a few mils to a precision of the nearest mil, you will
    get the same numerical result whether you are counting in units of one
    6000th, one 6400th or one 6283.1853...th of a circle.
    But woe betide the navigator who tries to calculate the reciprocal of a
    bearing in mils without knowing which kind of mil his instruments are
    calibrated in! I think I will stick to points. By comparison, they seem
    altogether simpler.
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

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