International System of Units, officially called the Système International d'Unités, or SI, system of units adopted by the 11th General Conference on Weights and Measures (1960). It is based on the metric system metric system, system of weights and measures planned in France and adopted there in 1799; it has since been adopted by most of the technologically developed countries of the world.
..... Click the link for more information. . The basic units of length, mass, and time are those of the mks system mks system, system of units of measurement based on the metric system and having the meter of length, the kilogram of mass, and the second of time as its fundamental units.
..... Click the link for more information. of metric units: the meter meter, abbr. m, fundamental unit of length in the metric system . The meter was originally defined as 1/10,000,000 of the distance between the equator and either pole; however, the original survey was inaccurate and the meter was later defined simply as the distance
..... Click the link for more information. , kilogram kilogram, abbr. kg, fundamental unit of mass in the metric system , defined as the mass of the International Prototype Kilogram, a platinum-iridium cylinder kept at Sèvres, France, near Paris.
..... Click the link for more information. , and second second, abbr. sec or s, fundamental unit of time in all systems of measurement. In practical terms, the second is 1/60 of a minute, 1/3,600 of an hour, or 1/86,400 of a day. Since the length of the day varies, however, the second must be defined in more precise terms.
..... Click the link for more information. . Other basic units are the ampere ampere (ăm`pēr), abbr. amp or A, basic unit of electric current.
..... Click the link for more information. of electric current, the kelvin of temperature (a degree of temperature measured on the Kelvin temperature scale Kelvin temperature scale, a temperature scale having an absolute zero below which temperatures do not exist. Absolute zero , or 0°K;, is the temperature at which molecular energy is a minimum, and it corresponds to a temperature of −273.
..... Click the link for more information. ), the candela, or candle candle, in weights and measures, unit of luminous intensity; it is defined as 1-60 of the intensity of a black body , or ideal radiator, at the temperature at which platinum solidifies (2,046°K;).
..... Click the link for more information. , of luminous intensity, and the mole mole, in chemistry, a quantity of particles of any type equal to Avogadro's number, or 6.02×10²³ particles. One gram-molecular weight of any molecular substance contains exactly one mole of molecules.
..... Click the link for more information. , used to measure the amount of a substance present. All other units are derived from these basic units.

Bibliography

See U.S. National Bureau of Standards, Spec. Pub. 330, International System of Units (1971).

International System of Units

or Système International d'Unités or SI system

International decimal system of weights and measures derived from and extending the metric system of units. Adopted by the 11th General Conference on Weights and Measures in 1960, it was developed to eliminate overlapping but different systems of units of measures fostered by rapid advances in science and technology in the 19th–20th centuries. Its fundamental units include the metre (m) for length, the kilogram (kg) for mass, and the second (sec) for time. Derived units include those for force (newton, N), energy (joule, J), and power (watt, W).