1^{st} (1889) |
kilogram
defined as mass of the international prototype kilogram (IPK) made
of platinum-iridium and kept at the International
Bureau of Weights and Measures (Bureau international des poids
et mesures), Sèvres,
France. International prototype metre sanctioned. |
2^{nd} (1897) |
No resolutions were passed by the 2nd CGPM. |
3^{rd} (1901) |
litre redefined as volume of
1 kg of water. Clarified that kilograms are units of mass,
"standard weight" defined, standard acceleration of gravity
defined endorsing use of grams force and making them
well-defined. |
4^{th} (1907) |
carat = 200 mg
adopted. |
5^{th} (1913) |
International Temperature Scale proposed. |
6^{th} (1921) |
Metre Convention revised. |
7^{th} (1927) |
Consultative Committee for Electricity (CCE) created. |
8^{th} (1933) |
Need for absolute electrical unit identified. |
9^{th} (1948) |
ampere, bar, coulomb, farad, henry, joule, newton, ohm, volt, watt, weber defined. Chose
degree Celsius from among
the three names then in use. l (lowercase L) adopted as symbol for
litre. Both the comma and dot on a line are accepted as decimal
marker symbols. Symbols for the stere and second changed [1]. The universal
return to the Long Scale numbering system was
proposed but not adopted. |
10^{th}
(1954) |
kelvin, standard
atmosphere defined. International System of Units (metre, kilogram, second, ampere, kelvin, candela) began. |
11^{th}
(1960) |
metre redefined in terms of wavelengths of light. Units: hertz, lumen, lux,
tesla adopted. New
metric system given the official symbol SI for
Système
International d'Unités, the "modernized metric
system". Prefixes pico-, nano-, micro-, mega-, giga- and tera- confirmed. |
12^{th}
(1964) |
original definition of litre
= 1 dm³ restored. atto-
and femto-
prefixes. |
13^{th}
(1967) |
second redefined as 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 at a
temperature of 0 K. Degree Kelvin renamed kelvin.
Candela redefined. |
14^{th}
(1971) |
new SI base
unit mole
defined. pascal,
siemens
approved. |
15^{th}
(1975) |
peta- and exa- prefixes. gray and becquerel radiological
units. |
16^{th}
(1979) |
candela, sievert defined. Both l and L
provisionally allowed as symbols for litre. |
17^{th}
(1983) |
metre redefined in terms of the speed of light, but keeps same
length. |
18^{th}
(1987) |
conventional values adopted for Josephson
constant, K_{J}, and von Klitzing constant,
R_{K}, preparing the way for alternative
definitions of the ampere and kilogram. |
19^{th}
(1991) |
new prefixes yocto-, zepto-, zetta- and yotta-. |
20^{th}
(1995) |
SI supplementary units (radian and steradian) become derived
units. |
21^{st}
(1999) |
new SI derived unit, the katal = mole per second, for the expression of catalytic
activity. |
22^{nd}
(2003) |
a comma or a dot on a line are reaffirmed as decimal marker
symbols, and not as grouping symbols in order to facilitate
reading; "numbers may be divided in groups of three in order to
facilitate reading; neither dots nor commas are ever inserted in
the spaces between groups". [2]. |
23^{rd}
(2007) |
clarification about the kelvin and thoughts about possible
revision of certain base units |