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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. Instances in use include the International System of ...
The metric system is a decimal -based system of measurement. The current international standard for the metric system is the International System of Units (Système international d'unités or SI), in which all units can be expressed in terms of seven base units: the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and ...
The systems formalised the concept of a collection of related units called a coherent system of units. In a coherent system, base units combine to define derived units without extra factors. [4]: 2 For example, using meters per second is coherent in a system that uses meter for length and seconds for time, but kilometre per hour is not coherent.
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]
Metrology is the scientific study of measurement. [1] It establishes a common understanding of units, crucial in linking human activities. [2] Modern metrology has its roots in the French Revolution 's political motivation to standardise units in France when a length standard taken from a natural source was proposed.
Standard (metrology) The international prototype of the kilogram (IPK) is an artefact or prototype that was defined to have a mass of exactly one kilogram. In metrology (the science of measurement), a standard (or etalon) is an object, system, or experiment that bears a defined relationship to a unit of measurement of a physical quantity. [1]
Units of measurement, Palazzo della Ragione, Padua. A unit of measurement, or unit of measure, is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. [1] Any other quantity of that kind can be expressed as a multiple of the unit of measurement.
The authority behind the SI system, the General Conference on Weights and Measures, recognised and acknowledged such traditions by compiling a list of non-SI units accepted for use with SI. [1] While not an SI-unit, the litre may be used with SI units. It is equivalent to (10 cm)3 = (1 dm)3 = 10−3 m3. Some units of time, angle, and legacy non ...