Metric System See also: Unit Prefixes System of Weights and measures planned in France and adopted there in 1799. Now used by most of the countries of the world, it is based on a unit of length called the meter (m) and a unit of mass called the kilogram (kg). The meter is now defined as the distance Light travels through a vacuum in 1/299,792,458 of a Second. The kilogram is defined as the mass of the International Prototype Kilogram, a Platinum-iridium cylinder kept at Sèvres, France, near Paris. Other metric units can be defined in terms of the meter and the kilogram. Fractions and multiples of the metric units are related to each other by powers of 10, allowing conversion from one unit to a multiple of it simply by shifting a decimal (see Numeration) point. This avoids the lengthy arithmetical operations required by the English Units of Measurement. The prefixes (see Metric Unit Prefixes) have been accepted for designating multiples and fractions of the meter, the gram (= 1/1000 kilogram), and other units. Several other systems of units based on the metric system have been in wide use. The cgs system uses the centimeter (= 1/100 meter) of length, the gram of Mass, and the second of Time as its fundamental units; other cgs units are the dyne of Force and the erg of Work or Energy. The meter-kilogram-second system uses the meter of length, the kilogram of mass, and the second of time as its fundamental units; other meter-kilogram-second units include the Newton of force, the Joule of work or energy, and the Watt of Power. The units of the meter-kilogram-second system are generally much larger and of a more practical size than the comparable units of the cgs system. Electric and magnetic units have been defined for both these systems. The International System of Units (officially called the Système International d'Unités, or SI) is a system of units adopted by the 11th General Conference on Weights and Measures (1960). Its basic units of length, mass, and time are those of the meter-kilogram-second system; other basic units are the Ampere of electric current, the kelvin of Temperature (a degree of temperature measured on the Kelvin temperature scale), the Candela of luminous intensity, and the Mole, used to measure the amount of asubstance present. All other units are derived from these basic units.