|
|
|
|
|||||
|
||||||
Subject: Re: The mil as a unit of angle.
From: Trevor J. Kenchington (Gadus@XXX.XXX)
Date: Tue Mar 11 2003 - 21:39:04 EST
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@XXX.XXX Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555Science Serving the Fisheries http://home.istar.ca/~gadus
|