Quantitative measurement of properties is reaquired for scientific investigation. Many properties of matter, such as length, area, volume, etc., are quantitative in nature. Any quantitative observation or measurement is represented by a number followed by units in which it is measured.
For example, length of a room can be represented as 6 m; here, 6 is the number and m denotesmetre, the unit in which the length is measured. Earlier, two different systems of measurement, i.e., the English System and the Metric System were being used in different parts of the world.
The metric system, which originated in France in late eighteenth century, was more convenient as it was based on the decimal system. Late, need of a common standard system was felt by the scientific community. Such a system was established in 1960 and is discussed in detail below.