The international system of measurement-units used throughout the sciences. SI units, which derive from metres, kilograms, and seconds, comprise seven basic units and two supplementary ones. Among the other base units are ampere (electric current) and mole (amount of a substance at molecular level). Derived SI units include joule (energy), pascal (pressure), becquerel (activity), and newton (force). (See APPENDIX 6: MEASUREMENTS IN MEDICINE.)
(Système International d’Unités) the internationally agreed system of units now in use for all scientific purposes. Based on the metre-kilogram-second system, SI units have seven base units and two supplementary units. Measurements of all other physical quantities are expressed in derived units, consisting of two or more base units. Tables 1.1 and 1.2 (Appendix 1) list the base units and the derived units having special names; all these units are defined in the dictionary.
Decimal multiples of SI units are expressed using specified prefixes; where possible a prefix representing 10 raised to a power that is a multiple of three should be used. Prefixes are listed in Table 1.3 (Appendix 1).
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