We are generally deal with a large number of physical quantities. Each physical quantity requires a separate unit for its measurement. As a result, we have to deal with a large number of units of different kinds. It is not practical to deal with as many units as there are physical quantities. To make measurements more scientific, convenient and uniform, the French Academy of Science in 1791 devised metric system of measurement based only the decimal system.
In 1901, G. Giorgi suggested a system of units based only meters, kilogram and second (MKS). In October 1960, the XII that General Conference of Weight and Measures adopted an International System of units. This system of units is known as the System International of Unites. The Units in this system of units are called SI units. The SI units have now been accepted in most countries.