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APPENDIX

International System of Units

The International System of Units (abbreviated SI from French: Système

international d'unités) is the modern form of the metric system. It
comprises a system of units of measurement devised around seven base
units and the convenience of the number ten. The SI was established in
1960, based on the meter-kilogram-second system, rather than the

centimeter-gram-second system, which, in turn, had several variants. The
SI has been declared to be an evolving system; thus prefixes and units are
created and unit definitions are modified through international agreement

as the technology of measurement progresses, and as the precision of
measurements improves.
SI is the world's most widely used system of measurement, used in both

everyday commerce and science. The system has been nearly globally
adopted with the United States being the only industrialised nation that
does not mainly use the metric system in its commercial and standards
[6]
activities. The United Kingdom has officially adopted a partial
metrication policy, with no intention of replacing imperial units entirely.
Canada has adopted it for many purposes but Imperial units, which are
used in the United States, are still legally permitted and remain in common

use throughout many sectors of Canadian society, particularly in the retail
food, buildings trades, and railways sectors.

The seven SI base units and the
interdependency of their definitions.
Clockwise from top: K-kelvin
(temperature), s-second (time), m-metre

(length), kg- kilogram (mass), cd-
candela (luminous intensity), mol-mole
(amount of substance) and A-ampere

(electric current). The second of time,
kelvin and kilogram are defined

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