LEGALLY RECOGNIZED in the UNITED STATES by the Metric Act of 1866 but devised by French scientists in a 1791 report to the French National Assembly, the metric system of measurement is the decimal system of weights and measures based on the meter, liter, and gram with the prefixes deci-, deca-, and kilo-. Originally not universally accepted, the metric system, designed to simplify the traditional system of weights and measurement used in Europe, replaced all the tradition units of measurement except the units of time and angle measure. The establishment of the metric system is widely regarded as the first step in the development of the International System of Units (SI), which links all systems of weight and measures.
The SI, the modern version of the metric system, was established in 1960 by the 11th General Conference on Weights and Measurements. This intergovernmental treaty organization, which itself was created by the Meter Convention in 1875, is the international authority that ensures the dissemination and modification of the metric system to reflect the latest changes in science and technology. Linked to the SI through the Meter Convention is the International Bureau of Weights and Measurements. This organization's mandate is to provide the basis for a single coherent system of measurement, through direct dissemination of units to coordinated international comparisons of national measurements standards, throughout the world.
The essential feature of the metric system of measurement, adopted by nearly every major industrialized country and viewed as a coherent system of units for physical science, is based on the length of a meter in relation to a platinum bar with a rectangular cross section and polished parallel ends. That is, the ideal behind the metric system was the use of only one measure per physically measured quality. Using the Earth as the measuring stick, the meter, intended to be one tenmillionth part of the quadrant of the Earth, was defined at the Meter Convention as the distance between the polished end faces at a specified temperature. This definition was based on a measurement of a meridian between Dunkirk, FRANCE, and Barcelona, ITALY.
Later used as the prototype for the base units of length and mass, the meter along with the kilogram, were the models for a three-dimensional mechanical unit system of measurement. Endorsed by the American Metric Association (now the United States Metric Association) in 1916, the length of the meter served as the U.S. primary metric system standard until 1960.
The advantages to using the metric system, outside of being the world standard of measurement, are numerous. A few of its greatest advantages are that it has only one unit for each type of measurement that is easy to use and pronounce, it is never necessary to convert from one unit to another within the metric system, and there are no conversion factors to memorize. In addition,the metric system uses decimals instead of fractions or mixed numbers.
In relation to the prefixes, one of the mathematical advantages to using the metric system is the combination metric terminology with its decimal organization. Because there are several prefixes associated with a decimal position, they can be attached to the base metric unit in order to create new metric units.
In 1975, the United States, through the Metric Conversion Act and the United States Metric Board, designated the metric system of measurement as the preferred system of weights and measurements for trade and commerce, and it directed federal agencies, during the construction of federal facilities, to convert, when feasible, to the metric system. The Metric Conversion Act, amended by Executive Order 12770 in 1991 by President George H.W. Bush, directed agencies to convert to the metric system of measurement, designating the Secretary of Commerce to direct and coordinate this effort. The hope is that through uniform use of the metric system there will no longer be misunderstanding, confusion, or error in universal weights and measurements.