![]() ![]() Some combinations, however, are more common than others. ![]() In general, prefixes are used with any metric unit, but may also be used with non-metric units. 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. Prefixes corresponding to powers of one thousand are usually preferred, however, units such as the hectopascal, hectare, decibel, centimetre, and centilitre, are commonly used. In addition to those listed in the everyday-use table, the SI includes standardised prefixes for 10 15 ( peta), 10 18 ( exa), 10 21 ( zetta), 10 24 ( yotta), 10 27 ( ronna), and 10 30 ( quetta) and for 10 −15 ( femto), 10 −18 ( atto), 10 −21 ( zepto), 10 −24 ( yocto), 10 −27 ( ronto), and 10 −30 ( quecto).ĭistance marker on the Rhine: 36 (XXXVI) myriametres from BaselĪlthough formerly in use, the SI disallows combining prefixes the * microkilogram or * centimillimetre, for example, are not permitted. The International Bureau of Weights and Measures has standardised twenty metric prefixes in resolutions dating from 1960 to 1991 for use with the International System of Units (SI). Some of the prefixes date back to the introduction of the metric system in the 1790s, but new prefixes have been added, and some have been revised. Each prefix has a unique symbol that is prepended to the unit symbol. The prefixes of the metric system precede a basic unit of measure to indicate a decadic multiple and fraction of a unit. ![]()
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