The seven basic SI units: 

(i) Metre (m): One metre is defined as the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second(1983). 

(ii) Kilogram(kg): It is the mass of a platinum-iridium cylinder (90% Pt and 10%Ir) whose height is equal to its diameter (each=3.9 cm) preserved at International Bureau of Weight and Measures at Sevres (1889). 

(iii) Second (s.): One second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the the two hyperfine levels of the ground state of the cesium-133 atom (1967). 

(iv) Ampere (A): One ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2*10^-7 newton per metre of length (1948). 

(v) Kelvin (K): One Kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water (1967). 

(vi) Candela(cd): Candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540*10²² hertz and that has a radiant intensity in that direction of 1/683 watt per steradian (1979). 

(vii) Mole (mol): One mole is the amount of substance of a system, which contains as many elementary antities as there are atoms in 0.012 kilogram of carbon-12(1971).