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The physical group size equivalent to m minutes of arc can be calculated as follows: group size = tan( m / 60 ) × distance. In the example previously given, for 1 minute of arc, and substituting 3,600 inches for 100 yards, 3,600 tan( 1 / 60 ) ≈ 1.047 inches. In metric units 1 MOA at 100 metres ≈ 2.908 centimetres.
Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10 −6 metre).
In firearm optics, where 0.1 mrad per click is the most common mrad based adjustment value, another common rule of thumb is that an adjustment of 1 / 10 mrad changes the impact as many centimeters as there are hundreds of meters. In other words, 1 cm at 100 meters, 2.25 cm at 225 meters, 0.5 cm at 50 meters, etc. See the table below
Metric prefixes; Text Symbol Factor or; yotta Y 10 24: 1 000 000 000 000 000 000 000 000: zetta Z 10 21: 1 000 000 000 000 000 000 000: exa E 10 18: 1 000 000 000 000 000 000: peta P 10 15: 1 000 000 000 000 000: tera T
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol ′, is a unit of angular measurement equal to 1 / 60 of one degree. [1] Since one degree is 1 / 360 of a turn, or complete rotation, one arcminute is 1 / 21 600 of a turn.
In practical applications it is often small: for example the triangles of geodetic survey typically have a spherical excess much less than 1' of arc. [14] On the Earth the excess of an equilateral triangle with sides 21.3 km (and area 393 km 2) is approximately 1 arc second. There are many formulae for the excess.
The micrometre (SI symbol: μm) is a unit of length in the metric system equal to 10 −6 metres ( 1 / 1 000 000 m = 0. 000 001 m). To help compare different orders of magnitude , this section lists some items with lengths between 10 −6 and 10 −5 m (between 1 and 10 micrometers , or μm).
The basic unit of length in the imperial and U.S. customary systems is the yard, defined as exactly 0.9144 m by international treaty in 1959. [2] [10] Common imperial units and U.S. customary units of length include: [11] thou or mil (1 ⁄ 1000 of an inch) inch (25.4 mm) foot (12 inches, 0.3048 m) yard (3 feet, 0.9144 m)