Article on other languages:
 |
del.icio.us |
 |
Digg |
 |
Furl |
 |
|
 |
Rojo |
| Add to OnlyWire |
An angular mil, also mil, is a unit of angle.
Contents |
Origin of the name
All versions of the angular mil are approximately the same size as a milliradian.
Use
The angular mil is commonly used by military organizations. Its relationship to the radian gives rise to the handy property that object of size s that subtends an angle θ angular mils is at a distance d = 1000s/θ. Alternatively, if the distance is known, we can determine the size of an object by s = θd/1000. The practical form of this that is easy to remember is: 1 mil at 1 km = 1 metre (2π/6.4 ≈ 0.98 m in NATO countries where mil is defined to be 1/6400 of a circle). Another example: 100 mils at 2 km = 200 metres.
In the general case, where neither the distance nor the object size is known, the formulae may be of little use. In practice, sizes of observed objects are known with reasonable accuracy since they are often people, buildings and vehicles. Using the formulae, distances of the objects can be readily calculated without a calculator. In military terms, distances are of course essential for artillery bombardments and estimations of journey times.
Artillery forward observers are usually trained to estimate the number of mils using combinations of fingers, their fist, and hand held at arm's length.
Markings on gunsights
Many telescopic sights used on rifles have reticles that are marked in angular mils, and these are generally called mil dot scopes. The mil dots serve two purposes, range estimation and trajectory correction. By determining how many angular mils an object of known size subtends, the distance to that object can be estimated with a fair degree of accuracy. Once the distance is known, the drop of the bullet at that range (see external ballistics), converted back into angular mils, can be used to adjust the aiming point. Generally mil dot scopes have both horizontal and vertical crosshairs marked; the horizontal and vertical marks are used for range estimation and the vertical marks for bullet drop compensation. Skilled shooters, however, can also use the horizontal dots to compensate for bullet drift due to wind. Mil dot scopes are most suited for long shots under uncertain conditions, such as those encountered by military snipers and varmint hunters. In both of those cases, the range to the target is not fixed and shots are taken at extreme ranges, so accurate compensation for bullet drop is required.
The four definitions of the angular mil
There are 2000π milliradians (≈ 6283.185 mrad) in a circle. So a milliradian is just over 1⁄6283 of a circle. Each of the definitions of the angular mil are similar to that value but are easier to divide into many parts.
- 1⁄6400 of a circle in NATO countries.
- 1⁄6283The “real” trigonometric unit of angular measurement of a circle in use by telescopic sight manufacturers using (stadiametric) rangefinding in reticles.
- 1⁄6000 of a circle in the former Soviet Union and Finland (Finland phasing out the standard in favour of the NATO standard).
- 1⁄6300 of a circle in Sweden. The Swedish term for this is streck, literally "line". Sweden has not been part of NATO nor the Warsaw Pact. Note however that Sweden is changing its map grid systems and angular measurement to those used by NATO, so the "streck" measurement is about to become obsolete.