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A system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce .
A collection of twelve things or units from Old French dozaine "a dozen, a number of twelve" in various usages, from doze (12c.) [2] Baker's dozen: 13 From the notion that a baker would include an extra item in a batch of twelve so as not to be accused of shortchanging a customer Half-dozen 6 Six of something Decade: 10
In 1824, these units were replaced with a single system based on the imperial gallon. [ a ] Originally defined as the volume of 10 pounds (4.54 kg) of distilled water (under certain conditions), [ b ] then redefined by the Weights and Measures Act 1985 to be exactly 4.546 09 L (277.4 cu in), the imperial gallon is close in size to the old ale ...
A base unit is a unit adopted for expressing a base quantity. 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 first group of metric units are those that are at present defined as units within the International System of Units (SI). In its most restrictive interpretation, this is what may be meant when the term metric unit is used. The unit one (1) is the unit of a quantity of dimension one. It is the neutral element of any system of units. [2]
Each conversion factor is chosen based on the relationship between one of the original units and one of the desired units (or some intermediary unit), before being rearranged to create a factor that cancels out the original unit. For example, as "mile" is the numerator in the original fraction and = , "mile" will need to be the ...
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The SI system after 1983, but before the 2019 revision: Dependence of base unit definitions on other base units (for example, the metre is defined as the distance travelled by light in a specific fraction of a second), with the constants of nature and artefacts used to define them (such as the mass of the IPK for the kilogram).