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Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property.
Metric units are units based on the metre, gram or second and decimal (power of ten) multiples or sub-multiples of these. According to Schadow and McDonald, [1] metric units, in general, are those units "defined 'in the spirit' of the metric system, that emerged in late 18th century France and was rapidly adopted by scientists and engineers.
Each variant of the metric system has a degree of coherence—the derived units are directly related to the base units without the need for intermediate conversion factors. [18] For example, in a coherent system the units of force , energy , and power are chosen so that the equations
The conversion between different SI units for one and the same physical quantity is always through a power of ten. This is why the SI (and metric systems more generally) are called decimal systems of measurement units. [10] The grouping formed by a prefix symbol attached to a unit symbol (e.g. ' km ', ' cm ') constitutes a new inseparable unit ...
The former Weights and Measures office in Seven Sisters, London (590 Seven Sisters Road). The imperial system of units, imperial system or imperial units (also known as British Imperial [1] or Exchequer Standards of 1826) is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments.
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).
Most of the units of measure have been adapted in one way or another since the Norman Conquest (1066). The units of linear measure have changed the least – the yard (which replaced the ell) and the chain were measures derived in England. The foot used by craftsmen supplanted the longer foot used in agriculture.
The other units of length and mass, and all units of area, volume, and derived units such as density were derived from these two base units. Mesures usuelles (French for customary measures) were a system of measurement introduced as a compromise between the metric system and traditional measurements. It was used in France from 1812 to 1839.