The metric system is a decimal system of weights and measures devised in Revolutionary France
in 1791 and based on the meter. The original
unit of mass was the gram,
the mass of a cubic centimeter of water at 4°C, the temperature of its
greatest density. Auxiliary units were to be formed by adding Greek prefixes
(see below) to the names
of the base units for their decimal multiples and Latin prefixes for their
decimal subdivisions. The metric system forms the basis of the physical
unit systems known as CGS units and MKS
units, the present SI (Systeme Internationale)
system being a development of the latter.
Metric prefixes are symbols used to specify orders of magnitude in the metric system of measurement,
using factors of 103 between steps. The mostly used prefixes
are shown in the illustration below.