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A similar system is used in natural gas sales in the United States: m (or M) for thousands and mm (or MM) for millions of British thermal units or therms, and in the oil industry, [30] where MMbbl is the symbol for "millions of barrels". This usage of the capital letter M for "thousand" is from Roman numerals, in which M means 1000. [31]
Milli (symbol m) is a unit prefix in the metric system denoting a factor of one thousandth (10 −3). [1] Proposed in 1793, [2] and adopted in 1795, the prefix comes from the Latin mille, meaning one thousand (the Latin plural is milia). Since 1960, the prefix is part of the International System of Units (SI).
The unit prefixes are always considered to be part of the unit, so that, e.g., in exponentiation, 1 km 2 means one square kilometre, not one thousand square metres, and 1 cm 3 means one cubic centimetre, not one hundredth of a cubic metre. In general, prefixes are used with any metric unit, but may also be used with non-metric units.
The Indian numbering system uses the named numbers common between the long and short scales up to ten thousand. For larger values, it includes named numbers at each multiple of 100; including lakh (10 5) and crore (10 7). [1] English also has words, such as zillion, that are used informally to mean large but unspecified amounts.
A derived unit is used for expressing any other quantity, and is a product of powers of base units. For example, in the modern metric system, length has the unit metre and time has the unit second, and speed has the derived unit metre per second.
The outhouse is a unit of area used in nuclear physics equal to 10 −6 barns (100 am 2 = 10 −34 m 2). The barn (b) is a unit of area used in nuclear physics equal to one hundred femtometres squared (100 fm 2 = 10 −28 m 2). The are (a) is a unit of area equal to 100 m 2. The decare (daa) is a unit of area equal to 1000 m 2.
It is used both as a unit of length (100 yd or 91.4 m, the length of the playing field excluding goal areas) and as a unit of area (57,600 sq ft or 5,350 m 2), about 1.32 acres (0.53 ha).
For example, 1 m/s = 1 m / (1 s) is the coherent derived unit for velocity. [1]: 139 With the exception of the kilogram (for which the prefix kilo- is required for a coherent unit), when prefixes are used with the coherent SI units, the resulting units are no longer coherent, because the prefix introduces a numerical factor other than one.