Quantity

Name

Sym

Definition
(CGPM)

length 
metre 
m 
The
metre is the length equal to 1 650763,73 wavelengths in vacuum
of the radiation corresponding to the transition between the levels
2 p10 and 5 d5,
of the krypton86 atom.[ 11th CGPM (1960), Resolution 6.]

mass 
kilogram 
kg 
The
kilogram is the mass of the international prototype of the kilogram
recognised by the CGPM and in the custody of the Bureau International
des Poids et Mesures, Sevres, France.
[ 1 st CGPM (1889).] 
time 
second 
s 
The
second is the duration of 9 192631 770 periods of the radiation
corresponding to the transition between the two hyperfine levels
of the ground state of the caesium133 atom. [13th CGPM (1967),
Resolution 1] 
electric
current 
ampere 
A 
The
ampere is that constant current which, if maintained in two straight
parallel conductors of cu rrent infinite length, of negligible
circular crosssection, and placed one metre apart in vacuum would
produce . between these conductors a force equal to 2 x 107 newton
per metre of length. [CIPM (1946), Resolution 2, approved by the
9th CGPM (1948).] 
thermo
dynamic temperature 
kelvin 
K 
The
kelvin, unit of thermodynamic temperature, is the fraction 1/273,16
of the thermodynamic temperature of the triple point of water.
[13th CGPM (1967), Resolution 4 ] 
amount
of substance 
mole 
mol 
The
mole is the amount of substance of a system which contains as
many elementary entities as there are atoms in 0,012 kg of carbon
12. [14th CGPM (1971), Resolution 3.] 
luminous
intensity 
candela 
cd 
The
candela is the luminous intensity, in the perpendicular direction
of a surface of 1/600000 square metre of a blackbody at the temperature
of freezing platinum under a pressure of 101 325 newtons per square
metre. [13th CGPM (1967), Reso'n 5.] 
NOTES:
(i) The unit kelvin and its symbol K are also used
to indicate temperature intervals or temperature differences.
Besides thermodynamic temperature (symbol T), expressed in kelvins,
Celsius temperature (symbol t) is also used. Celsius temperature
is defined by the equation: t = T  T0 where T0 = 273,15 K by
definition. Celsius temperature is in general expressed in degrees
Celsius (symbol ^{o}C). The unit
"degree Celsius" is therefore equal to the unit "kelvin" and an
interval or difference in Celsius temperature is also expressed
in degrees Celsius (^{o}C). Note
that the Celsius temperature of the triple point of water is 0,01
^{o}C, which accounts for the factor
273,16 in the definition of the kelvin.
(ii) Whenever the mole is used, the elementary entities must be
specified, and may be atoms, molecules, ions, electrons, other
particles or specified groups of such particles.
(iii) With the object of removing the ambiguity which still occurred
in the common use of the word "weight", the 3rd CGPM (1901) declared:
"The kilogram is the unit of mass [and not of weight or of force];
it is equal to the mass of the international prototype of the
kilogram."

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