# SI

Abbreviation of ‘Système International d'Unités’, the modern form of the metric system of measurement. The SI units are strictly the metre, kilogram, second, ampere, Kelvin, candela and mole. Other units are derived including hectare, pascal, newton, joule, watt. Prefixes of magnitude include milli- (10 to the power -3), kilo- (10 power 3), mega- (10 power 6), giga- (10 power 9) and tera- (10 power 12).

This definition is abridged from **A – Z of tree terms: A companion to British arboriculture**.

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