09-05-2014, 08:37 PM (This post was last modified: 09-05-2014 11:31 PM by Richard Wagner.)
Post: #26
 Richard Wagner Junior Member Posts: 18 Joined: Aug 2014
the following definition(s) is taken from:
http://en.wikipedia.org/wiki/Angle

Mil (n = 6000–6400)
The mil is any of several units that are approximately equal to a milliradian. There are several definitions ranging from 0.05625 to 0.06 degrees (3.375 to 3.6 minutes), with the milliradian being approximately 0.05729578 degrees (3.43775 minutes). In NATO countries, it is defined as 1/6400th of a circle. Its value is approximately equal to the angle subtended by a width of 1 metre as seen from 1 km away (2π / 6400 = 0.0009817… ≒ 1/1000).

That says more than my expensive math reference books on my shelves ever told me. :-)

That web page also explains Tr and other concepts as well!!
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and from: http://boards.straightdope.com/sdmb/show...p?t=302538
we have this wonderful revelation:

why does anyone want to divide a right angle into 100 grads instead of 90 degrees?

grads are a decimal unit, and are subdivided into simple 100ths, just like the meter is subdivided into cetimeters..Degrees are not decimal units--they are subdivided into 60 minutes and then another 60 seconds.So every time you want to do a simple calculation (say, adding two angles), you have to do first do TWO extra steps--convert the seconds into decimal minutes, then convert the decimalized minutes into decimal degrees. (most pocket calculators have a simple button that does this, but it still requires you to press an extra button before doing the actual calculation that you want to complete.

try this example--add two angles : 75 degrees, 45 minutes, 20 seconds plus 25 degrees 15 minutes 10 seconds.
Which is easier?

Land surveyors (those guys you see on the side of the road with an instrument mounted on a tripod) make hundreds or even thousands of angle measurements during a day's work.

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and still more evidence Grad is cherished:
http://mathforum.org/library/drmath/view/55451.html

http://www.unc.edu/~rowlett/units/dictG.html

a unit of angle measurement equal to 1/400 circle, 0.01 right angle,
0.9 degrees, or 54'. This unit was introduced in France, where it is
called the grade, in the early years of the metric system. The grad
is the English version, apparently introduced by engineers around
1900. The name gon is used for this unit in German, Swedish, and
other northern European languages in which the word grad means
degree. Although many calculators will display angle measurements in
grads as well as degrees or radians, it is difficult to find actual

http://jeff560.tripod.com/g.html

GRAD or GRADE originally meant one ninetieth of a right angle, but
the term is now used primarily to refer to one hundredth of a right
angle.

Gradus is a Latin word equivalent to "degree."

Nicole Oresme called the difference between two successive
latitudines a gradus (Smith vol. 2, page 319).

The OED2 shows a use of grade in English in about 1511, referring
to one-ninetieth of a right angle.

The OED2 shows a use of grade, meaning one-hundredth of a right
angle, in 1801 in Dupre Neolog. Fr. Dict. 127: "Grade .. the
grade, or decimal degree of the meridian."

The term may have been used in the modern sense in the unpublished

In 1857, Mathematical Dictionary and Cyclopedia of Mathematical
Science has: "The French have proposed to divide the right angle
into 100 equal parts, called grades, but the suggestion has not

Searching for other references, I found these:

NIMA: Datums, Ellipsoids, Grids, and Grid Reference Systems
http://cartome.org/nima-grids.htm

Some foreign produced maps may use the centesimal (decimal) system
of angular measurement (the division of a full circle into 400
seconds).
...
Geographic coordinates are given in terms of angular measurement,
usually in degrees, minutes, and seconds but occasionally in grads.

Gregor Shapiro helped me find this one:

Silva: General Compass InformationReference Systems
http://www.silva.se/outdoor/products/comp_general.htm

Normal graduation is 360o. For Scandinavian countries 400 gon
is also used. Military graduation 6400' or 6300' (Sweden).
Often both 360o and 6400' are used, i.e. double graduation.
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By pasting specific text here, this message is now a complete reference
onto itself of mils and grads. Also, webpages have a notorious history of disappearing eventually.