International System of Units
Abbreviation | SI units |
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Synonym | Metric system of units |
Definition | A set of measurement units defined accordance to the corresponding International System of Quantities (ISQ) |
Scope |
The system is founded on 7 base SI units corresponding to the 7 base kinds-of-quantity. The base units can be combined in various ways forming derived units. Note: In laboratory medicine, number of entities with the corresponding base unit, 1, is well recognized, although it does not belong to the SI units. |
Rules |
The rules for the expression of quantities in SI units are to ensure consistent and legible formatting, including:
IUPAC publishes detailed recommendations for properties, units and formats for the reporting of clinical laboratory results in the “Silver Book” (Compendium of Terminology and Nomenclature of Properties in the Clinical Laboratory Sciences). Note: Volume should be expressed litre (L, mL, µL, etc) rather than the strict SI unit of volume, the cubic metre (m3). |
Reference |
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Base units |
Note: Number of entities does not belong to the ISQ, but is an accepted and neccessary kind-of-quantity in laboratory medicine. |
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Derived units |
Note: The table represents only a fraction of derived units |
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Reference |
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Abbreviation | SI units |
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Synonym | SI Units, Système international (d’unités) |
Description |
The SI units system is the most widely used system of measurement in the world, administered by the Bureau International des Poids et Mesures (BIPM). There are seven base units of measurement, and by 20th May 2019 each will be defined by physical constants in nature. For example, the second will be defined as a fixed number of transition of the caesium-133 atom, the metre will be based on the speed of light in a vacuum per unit time, the mole will equal a fixed number of elements/molecules (“the Avogadro constant”). There are rules for the expression of quantities in SI units to ensure consistent and legible formatting, including:
IUPAC publishes detailed recommendations for properties, units and formats for the reporting of clinical laboratory results in the “Silver Book” (Compendium of Terminology and Nomenclature of Properties in the Clinical Laboratory Sciences). Substance concentrations should be expressed in moles per litre (mol/L, mmol/L, umol/L, etc) rather than the strict SI unit of volume, the cubic metre. |
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