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The SI system after the 2019 definition: Base units as defined in terms of physical constants and other base units. Here, means is used in the definition of . The SI system after 1983, but before the 2019 redefinition: Base unit definitions in terms of 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 ...
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).
[a] This system underlies the International System of Units (SI) [b] but does not itself determine the units of measurement used for the quantities. The system is formally described in a multi-part ISO standard ISO/IEC 80000 (which also defines many other quantities used in science and technology), first completed in 2009 and subsequently ...
ISO 80000-1:2022 revised ISO 80000-1:2009, which replaced ISO 31-0:1992 and ISO 1000:1992. [22] This document gives general information and definitions concerning quantities, systems of quantities, units, quantity and unit symbols, and coherent unit systems, especially the International System of Quantities (ISQ). [3]
The International System of Units, internationally known by the abbreviation SI (from French Système international d'unités), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official status in nearly every country in the world, employed in science ...
The International System of Units (SI) defines seven base units: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity. [24] By convention, each of these units are considered to be mutually independent and can be constructed directly from their defining constants.
The ISO 31 and IEC 60027 Standards were revised by the two standardization organizations in collaboration (, ) to integrate both standards into a joint standard ISO/IEC 80000 - Quantities and Units in which the quantities and equations used with SI are to be referred as the International System of Quantities (ISQ). ISO/IEC 80000 supersedes both ...
The first table lists the fundamental quantities used in the International System of Units to define the physical dimension of physical quantities for dimensional analysis. The second table lists the derived physical quantities. Derived quantities can be expressed in terms of the base quantities.