# General Conference on Weights and Measures

The International General Conference on Weights and Measures (from the French: Conférence Générale des Poids et Mesures ; short: CGPM ) is the conference of the plenipotentiaries of the member states of the Meter Convention . It is the decision-making body of the Meter Convention and meets regularly at the headquarters of the International Bureau of Weights and Measures (BIPM) in the Paris suburb of Sèvres . It is here that resolutions on fundamental issues relating to the Meter Convention and the metric system of units and, since 1960, the international system of units (SI) are passed. Reports of meetings and resolutions are published by the International Bureau. In addition, the General Conference elects the 18 members of the International Committee for Weights and Measures (CIPM) . The convention provides for a meeting no more than six years apart, it is convened by the International Committee and is chaired by the President of the French Academy of Sciences . Germany, Austria and Switzerland have been members of the General Conference as the first signatories to the Convention since it first met in 1889.

The conference has been held every four (or three) years since 1960. As of November 2018, 60 states are (full) members of the Meter Convention, a further 42 associated states are not members of the General Conference.

## Chronology of the conferences

No. year Important decisions
01 1889 The prototypes for kilograms and meters selected by the CIPM (International Committee for Weights and Measures) are confirmed.
02 1895 No resolutions.
03 1901 The unit of volume for precision measurements should be the liter , now defined as the volume of 1 kg of pure water of maximum density at normal atmospheric pressure.
The kilogram is a unit of mass and at the same time the mass of the international prototype of the kilogram.
The word “ weight ” does not mean a mass, but a force. Is the weight of a body is the product of its mass and the acceleration of gravity, and in particular is its standard weight the product of mass and standard acceleration (980.665 cm / s²).
04th 1907 Metric carat = 200 mg adopted.
05 1913 International temperature unit proposed.
06th 1921 The text of the meter convention will be changed.
07th 1927 Small changes are made to the definition of the meter.
The Advisory Committee on Electricity (CCE) is established as the first advisory committee.
08th 1933 Determined the need for an absolute unit for electrical current.
09 1948 Ampere , bar , Coulomb , Farad , Henry , Joule , Newton , Ohm , volt , watt , Weber defined.
Unit name " degrees Celsius " specified (previously, "centigrades" and "centesimal degrees" were also common).
l (small L) assumed as a symbol for liter.
Set notation of numbers and unit symbols. Decimal comma and point are allowed.
"St" for the star (previously: "st" and "s") and "s" for the second (previously: "s", "sec", "sec.") Are specified as the only, unambiguous unit symbols .
The proposal to return to the long scale for designating powers of ten greater than a million was not accepted .
The CIPM is commissioned to develop recommendations for the establishment of a single practical system of units.
10 1954 Standard value of atmospheric pressure set.
A practical system of units to be used in international traffic should be based on six basic units: meter (size: length), kilogram (mass), second (time), ampere (electrical current), degrees Kelvin (thermodynamic temperature) and candela (light intensity).
11 1960 Meter defined as a function of the wavelength of light. The units Hertz , Lumen , Lux and Tesla are adopted. The new metric system is given the official symbol SI for Système International d'Unités , the “modern metric system”.
The unit prefixes pico , nano , micro , mega , giga and tera are confirmed.
12 1964 Original definition, 1 liter = 1 dm³, restored.
Introduction of the SI prefixes Atto- and Femto- .
13 1967 Renamed degrees Kelvin to Kelvin .
The second is defined by the radiation emitted by atoms of the nuclide 133 Cs (“ atomic second ”).
14th 1971 The mole is introduced as the new SI base unit.
Pascal (Pa) and Siemens (S) are accepted as special names of derived SI units.
15th 1975 The SI prefixes Peta- and Exa- as well as the special names for the derived units Becquerel (Bq) and Gray (Gy) are added.
16 1979 The candela is being redefined and linked to the watt .
Inclusion of the Sievert (Sv) as a derived unit with its own name for the specification of equivalent doses in the field of radiation protection .
Exception rule for the unit liter : in addition to the unit symbol l, L is also permitted.
17th 1983 Meter redefined by giving the speed of light a fixed value.
18th 1987 Conventional values ​​for Josephson's constant K J and Von Klitzing's constant R K are adopted to pave the way for alternative definitions of amps and kilograms.
19th 1991 New SI prefixes Yokto- , Zepto- , Zetta- and Yotta- .
20th 1995 The supplementary SI units radians and steradian are declared to be derived units.
21st 1999 Inclusion of the Katal (kat) as a coherent derived SI unit of the catalytic activity with a special name.
22nd 2003 The comma and the point at line height are confirmed as decimal separators ; they must not be used to structure sequences of digits.
23 2007 Determination of the isotopic composition of the water for the definition of the Kelvin .
24 2011 Presentation of the planned reform (decided in 2018)
25th 2014 No resolutions to measure
26th 2018 Revision of the system of units with effect from May 20, 2019: All units are based on natural constants. Avogadro's constant , Boltzmann's constant , elementary charge and Planck's constant of action have fixed values.

## Individual evidence

1. Outcomes of the General Conference , BIPM website; accessed November 16, 2018.
2. Member States , BIPM website; accessed November 16, 2018.
3. 26th CGPM (2018) - Resolutions adopted / Résolutions adoptées. (PDF; 1.2 MB) Versailles 13–16 November 2018. In: bipm.org. Bureau International des Poids et Mesures, November 19, 2018, pp. 2–5 , accessed on April 28, 2019 (English, French).
4. Jens Simon: Natural constants as the main character - PTB.de. General Conference on Weights and Measures (CGPM) adopts revision of the International System of Units. In: PTB.de. Physikalisch-Technische Bundesanstalt, November 16, 2018, accessed on April 28, 2019 .