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.