Ontology

Definition:

"An electric current unit which is equal to the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2 x 10^[-7] newton per meter of length." [BIPM:BIPM, NIST:NIST]

Definition:

"A luminous intensity unit which equal to the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian." [BIPM:BIPM, NIST:NIST]

Definition:

"A thermodynamic temperature unit which is equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water." [BIPM:BIPM, NIST:NIST]

Definition:

"A mass unit which is equal to the mass of the International Prototype Kilogram kept by the BIPM at Svres, France." [BIPM:BIPM, NIST:NIST]

Definition:

"A length unit which is equal to the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second." [BIPM:BIPM, NIST:NIST]

Definition:

"A time unit which is equal to the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom." [BIPM:BIPM, NIST:NIST]