Length: meter (m): The SI unit of length, being the length of the path traveled by light in vacuum during a time interval of 1/(2.997 924 58 x 10^8) second.
Mass: kilogram (kg): The SI unit of mass defined as a mass equal to that of the international platinum-iridium prototype kept by the International Bureau of Weights and Measures at Sevres, near Paris. (This is the only base unit still defined by an artifact.)
Time: second (s): The SI unit of time equal to the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom.
Electric Current: ampere (A): The SI unit of electric current. The constant current that, maintained in two straight parallel infinite conductors of negligible cross section placed one metre apart in vacuum, would produce a force between the conductors of 2 x 10^-7 N m^-1.
Temperature: kelvin (K): The SI unit of thermodynamic temperature equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The magnitude of the kelvin is equal to that of the degree celsius (centigrade), but a temperature expressed in degrees celsius is numerically equal to the temperature in kelvins less 273.15. The former name _degree kelvin_ (symbol degK) became obsolete by international agreement in 1967.
Luminous Intensity: candela (cd): The SI unit of luminous intensity equal to the luminous intensity in the perpendicular direction of the black-body radiation from an area of 1/600 000 square metre at the temperature of freezing platinum (2042 kelvins) under a pressure of 101 325 pascals.
Amount of Substance: mole (mol): The SI unit of amount of substance. It is equal to the amount of substance that contains as many elementary units as there are atoms of 0.012 kg of carbon-12. The elementary units may be atoms, molecules, ions, radicals, electrons, etc., and must be specified.
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