History

Chronology: 150 years of international use of the Metric System
“For all time, for all people”

The law of 18 Germinal An III (Republican calendar) established the metric system in France.
Two platinum standards representing the metre and the kilogram were deposited in the French National Archives.
A Comité des poids, mesures et monnaies was established during the International Exhibition in Paris and called for the international adoption of the metric system.
The Europaische Gradmessung (European Degree Measurement) at its second meeting in Berlin called for the creation of a European Bureau of Weights and Measures, a new international prototype and the international adoption of the metric system for geodetic measurement.
Following the recommendation of the Bureau des longitudes, the French Academy of Sciences and the Academy of Saint-Petersburg, Napoleon III invited States to send representatives to agree on the international adoption of the metric system.
The International Commission of the Metre met in Paris for the first time at the Conservatoire imperial des arts et métiers a few days after the outbreak between France and Prussia. 
The work of the International Metre Commission restarted.
First official casting of a 20-kilogram platinum-iridium ingot from Matthey by Henri Sainte-Claire Deville in his laboratory at the École Normale in Paris during the 6th session of the French Section of the Metre Commission in the presence of Louis Pasteur, Minister Teisserenc de Bort and the President of the Republic, Adolphe Thiers.
250 kilograms of platinum-iridium used for several national prototypes of the metre was casted at the Conservatoire des arts et métiers.
Diplomatic Conference of the Metre.
The Metre Convention was signed in Paris by representatives of seventeen nations the BIPM. This international treaty was signed in the Salon de l’Horloge at the Ministry of Foreign Affairs where the Convention on Telegraphy, which establish the International Union for Telegraphy, was signed ten years before. 
Adolphe Hirsch agreed on the design for a macaron (or formal seal).  The dictum “Keep the measure” on the seal emphasized the role of the organization in the preservation of the International Prototypes. It outlined principles of neutrality, fairness, and impartiality, that still underpin the principles of the BIPM today.
Gilberto Govi was appointed as first Director of the BIPM. Adolphe Hirsch, Director of the Neuchâtel Observatory and Secretary of the International Association of Geodesy was elected as CIPM Secretary and Carlos Ibáñez e Ibáñez de Ibero was elected as the first CIPM President.
The first General Conference on Weights and Measures (CGPM) sanctioned the new international prototypes of the metre and the kilogram: an important milestone towards the international unification of the metric system.
Albert Michelson, supported by René Benoît, Director of the BIPM, made the first determination of the value of the metre in terms of wavelength using the red light of cadmium with the interferometer he brought from the US in the BIPM laboratories. The results were published in 1895 in the Travaux et Mémoires du Bureau international des poids et mesures, the scientific publication of the BIPM. This publication was sent to the most eminent scientists of the time. 
Charles-Édouard Guillaume discovered an iron-nickel alloy (64 % iron and 36 % nickel) with a near-zero coefficient of thermal expansion. Invar transformed the practices for geodesy giving the BIPM a central role for international geodetic measurements. 
Declaration on distinguishing mass and weight and on the conventional value of the standard acceleration due to gravity. 
The Royal Observatory at Kew, near London, the absolute reference at the time, awarded Paul Ditisheim the "world chronometric record" with a timepiece equipped with a Guillaume balance.
The first international radium standard was deposited at the BIPM by Marie Curie and André Debierne on behalf of the International Radium Commission.  The first international standard prepared by Marie Curie was the basis of the international measurement system for about 50 years.
Charles-Édouard Guillaume was awarded the Nobel Prize in physics “in recognition of the service he has rendered to precision measurements in Physics by his discovery of anomalies in nickel steel alloys.” His research revolutionized work for length measurement, improved time-measuring instruments and had a significant effect on incandescent light bulbs. Balance springs in invar and élinvar equipped respectively 10 000 000 of watches for the first invar springs of 50 000 000 of watches for the élinvar spring. Five members of the CIPM (Albert Michelson (1907), Pieter Zeeman (1902), Karl Manne Siegbahn (1924), Louis de Broglie (1929) et Kai Manne Siegbahn (1981)) were awarded the Nobel Prize in Physics. Along with Michelson, Charles-Édouard Guillaume is the only physicist to have won the Nobel Prize for work carried out in the BIPM’s laboratories.
The Metre Convention was revised to extend the activities to electricity, photometry and radiometry. A first sept towards the extension of the activities to all fields.
The first Consultative Committee was set up: The Consultative Committee for Electricity (CCE) which integrated as a first stage thermometry met for the first time in 1928. Between 1930 and 1933 the CCE dealt with matters concerning photometry.  Its name was changed to Consultative Committee for Electricity and Magnetism by the CIPM in 1997.
Creation of the Consultative Committee for Photometry (CCP). CCP met for the first time in 1937 and became the Consultative Committee for Photometry and Radiometry (CCPR) in October 1971.
The Consultative Committee for thermometry was set up and held its first meeting in 1939. 
Definition of photometric units, new candle and new lumen (with entry into force on 1 January 1948).
The 9th CGPM requested the CIPM to launch an international survey, the outcome of which was to be used to formulate recommendations for a single practical system of measurement units, suitable for adoption by all countries. The CGPM adopted the triple point of water as the thermodynamic reference point, and adopted the zero of Celsius temperature to be 0.01 degrees below the triple point.
The Consultative Committee for thermometry was set up and held its first meeting in 1939. The Consultative Committee for the Definition of the Metre (CCDM) was established and held its first meeting the year after. The CCDM was renamed in 1997 to become the Consultative Committee for Length (CCL).
The CGPM approved the introduction of the ampere, the kelvin and the candela as base units for electric current, thermodynamic temperature and luminous intensity respectively. A Commission of System of Units was set up.
The CIPM adopted a new definition of the second based on the set up of the Consultative Committee for the Definition of the Second (CCDS) renamed Consultative Committee for Time and Frequency in 1997).
The Consultative Committee for the Definition of the second (CCDS) held its first meeting at the BIPM. The atomic standards were discussed at this meeting.
The Consultative Committee for the Standards of Measurement of Ionizing Radiation (CCEMRI) (the name was changed to Consultative Committee for Ionizing Radiation (CCRI) in 1997) met for the first time on 13 April 1959.
The 11th CGPM adopted the name of the International System of Units (SI) for the system based on six base units: the metre, the kilogram, the second, the ampere, the kelvin and the candela. The 11th CGPM adopted the redefinition of the metre in terms of krypton 86 radiation and sanctioned the new definition of the second proposed by the CIPM and given by the International Astronomical Union. The definition was based on the tropical year 1900. Experimental work, however, had already shown that an atomic standard of time, based on a transition between two energy levels of an atom or a molecule, could be realized and reproduced much more accurately.
Set up of the Ionizing Radiation Section at the BIPM.
Inauguration of a new building with laboratories for Ionizing Radiation activities.
First meeting of the he Consultative Committee for Units (CCU), which was set up in 1964 and replaced the Commission of System of Units.
Considering that a very precise definition of the unit of time was indispensable for science and technology, the CGPM at its 13th meeting (1967-1968) adopted a new definition of the second referenced to the frequency of the ground state hyperfine transition in the caesium-133 atom. An important change of paradigm: the unit of time moved from physics to astronomy. It also adopted a formal definition of the kelvin as unit of thermodynamic temperature and defined the candela, symbol cd, in terms of a black body radiator.
The 14th CGPM added a new unit to the SI: the mole as the unit for amount of substance. The mole became the 7th unit of the SI.
The BIPM celebrated its 100th anniversary. The 15th CGPM was held in May to celebrate this important milestone and the delegates were received by the President of the French Republic at the Palais de l’Élysée. An important exhibition was organised at the Palais de la Découverte in Paris. The CGPM endorsed the use of Coordinated Universal Time (UTC).
The 16th CGPM redefined the candela in terms of monochromatic radiation.
The Consultative Committee for Mass and Related Quantities (CCM) was established.
For the first time a definition of a base unit of the SI was based on a fundamental constant: the speed of light. The metre was henceforth the length of the path travelled by light in vacuum during a specific fraction of a second.
The BIPM Time Section was set up.
Transfer of the activities of the International Time Bureau (BIH) including International Atomic Time (TAI) at the BIPM.
The Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) was set up.
The Mutual Recognition Arrangement (MRA) drawn up by the International Committee of Weights and Measures (CIPM) (CIPM MRA) was established. The CIPM MRA is a platform that provides the institutional and technical framework for National Metrology Institutes around the world to recognize each other’s measurement standards and calibration certificates. Its supporting data, representation of measurement capabilities, and quality infrastructure are rigorously validated by NMIs and other participants in the international measurement system. 251 institutes participate in the CIPM MRA, comprising 97 National Metrology Institutes, 4 international organizations and 150 designated institutes.
Launch of the Key Comparison Database (KCDB). 100 key comparisons in Appendix B were published online on 30 November 1999 followed by the first entries in Appendix C on 12 December 1999. The KCDB was the result of a collaboration between Robert Watters and Claudine Thomas at the BIPM. The KCDB was entirely run by the BIPM as from 2003.
Creation of the Consultative Committee for Acoustics, Ultrasound and Vibration (CCAUV).
Following the decision of the CGPM at its 21st meeting in 1999, a Chemistry Section was set up at the BIPM.
A new building was inaugurated improving the facilities for hosting international meetings showing the importance of coordination activities.
The BIPM launched the Capacity Building and Knowledge transfer programme.
 Four base units of the SI were redefined, including the unit of mass, which was the last unit to be defined by an artefact: the International Prototype of the Kilogramme was the definition of the unit of mass since 1889. As from November 2018, the SI is defined in terms of a set of seven defining constants.
• the caesium hyperfine frequency Δν Cs
• the speed of light in vacuum c
• the Planck constant h
• the elementary charge e
• the Boltzmann constant k
• the Avogadro constant NA
• the luminous efficacy of a defined visible radiation Kcd
Entry in force of the revised SI.
The 27th meeting of the CGPM adopted a resolution on universal adherence to the Metre Convention to further strengthening the role of the BIPM and to facilitate wider participation in its activities, thus achieving lasting and universal adherence to the Metre Convention.
At its 42nd General Conference in November 2023, UNESCO officially recognized World Metrology Day (WMD), which takes place every year on 20 May. WMD celebrates every year the signing in Paris of the Metre Convention on 20 May 1875 by the representatives of seventeen nations.
Establishment of two forums:
- CIPM Sectorial Task Group on Climate Change and Environment (CIPM-STG-CENV) to provide a global focal point for metrology activities related to climate change and environment.
- Forum on Metrology and Digitalisation to advise the CIPM on the SI Digital Framework and the wider implications of the global digital transformation for metrology and for the international Quality Infrastructure
Launch of the SI Reference Point. The SI Reference Point is a set of tools designed to provide an authoritative digital reference for the International System of Units (SI), traditionally published by the BIPM in the form of the SI Brochure. The SI Reference Point is designed to be fully FAIR* and machine actionable.
150th anniversary of the Metre Convention.
To be continued
New definition of the second
Universal adherence to the Metre Convention
Digital transformation

“From the units to the universe”