Knowra International System of Quantities International System of Quantities The International System of Quantities (ISQ) is a coherent system that defines physical quantities and their relationships independently of the units used to measure them. It underlies the International System of Units (SI).
Physical quantity : A property that can be expressed as a number and a reference, such as a unit. The ISQ classifies physical quantities and specifies how they relate.
International System of Quantities base quantities : The seven ISQ base quantities: time, length, mass, electric current, thermodynamic temperature, amount of substance, and luminous intensity. These form the chosen independent foundation for the ISQ.
Unit of measurement : A defined reference magnitude used to express the value of a quantity. An ISQ quantity is not the unit chosen to measure it.
Metrology : The science of measurement, including units, measurement procedures, and uncertainty. Metrology uses the ISQ to organize the quantities measured across disciplines.
Base quantity : A quantity in a chosen set treated as independent within a system of quantities. The ISQ builds its quantity relationships from seven selected bases.
International System of Quantities base equations : The defining equations that relate the seven ISQ base quantities to one another. They establish the ISQ's quantity structure independently of unit choices.
International System of Units : The internationally agreed system of measurement units, including seven base units and units derived from them. The SI assigns units; the ISQ defines the quantities those units measure.
International vocabulary of metrology : A jointly maintained vocabulary defining fundamental concepts in metrology. Its terminology formalizes distinctions among quantity, unit, and measurement.
Derived quantity : A quantity defined from other quantities through an equation. ISQ equations express derived quantities through base quantities.
Dimensional analysis : A method for checking physical equations and scaling relations by comparing dimensions. ISQ dimensions make this method possible without specifying measurement units.
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