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A chronology of the metric system


Important dates and associated documents in the history of the modern metric system

(In this list, U.S. laws and regulations are emphasized with a colored background)

1585
In his book "The Tenth" Simon Stevin suggests that a decimal system should be used for weights and measures, coinage, and divisions of the degree of arc.
1670
Authorities give credit for originating the metric system to Gabriel Mouton, a French vicar, on about this date.
1790
Thomas Jefferson proposed a decimal-based measurement system for the United States.
France's Louis XVI authorized scientific investigations aimed at a reform of French weights and measures. These investigations led to the development of the first "metric" system.
1792
The U.S. Mint was formed to produce the world's first decimal currency (the U.S. dollar consisting of 100 cents).
1795
France officially adopted the metric system.
1812
Napoleon temporarily suspended the compulsory provisions of the 1795 metric system adoption.
1840
The metric system reinstated as the compulsory system in France.
1866
The use of the metric system made legal in the United States by the Metric Act of 1866 (Public Law 39-183). This law made it unlawful to refuse to trade or deal in metric quantities.
1875
The Convention of the Metre signed on 20 May 1875 in Paris by 17 nations, including the United States. The Meter Convention, often called the Treaty of the Meter in the United States, provided for improved metric weights and measures and the establishment of the General Conference on Weights and Measures (CGPM) devoted to international agreement on matters of weights and measures. To recognize this anniversary, 20 May is now World Metrology Day, as found on the Metric events and anniversaries page.
1889
As a result of the Metre Convention, the U.S. received a prototype meter and kilogram to be used as measurement standards.
1893
These metric prototypes were declared "fundamental standards of length and mass" in the Mendenhall Order. Since that date, the yard, pound, etc. have been officially defined in terms of the metric system.
1916
The Metric Association formed as a non-profit organization advocating adoption of the metric system in U.S. commerce and education. The organizational name started as the American Metric Association and was changed to the U.S. Metric Association (USMA) in 1974.
1920
The Metric Association published its first metric style guide. [Its current edition is now available as Guide to the Use of the Metric System (SI)]
1954
The International System of Units began its development at the 10th CGPM. Six of the new metric base units were adopted.
1958
A conference of English-speaking nations agreed to unify their standards of length and mass, and define them in terms of metric measures. The American yard was shortened and the imperial yard was lengthened as a result. The new conversion factors were announced in the Federal Register (v. 24(128), 1959-Jul-01, p. 5348-5349).
1960
The General Conference on Weights and Measures (CGPM) adopts the name Système International d'Unités, with the international abbreviation SI, for the metric system and lays down rules for prefixes, derived units, and other matters, specifying six base units (meter, kilogram, second, ampere, kelvin, candela).
The meter is redefined in terms of a wavelength of light emitted by krypton atoms, replacing the 1889 prototype bar of platinum-iridium (see the history of definitions of the meter).
1964
The National Bureau of Standards (NBS) made the metric system its standard "except when the use of these units would obviously impair communication or reduce the usefulness of a report."
1968
Public Law 90-472 authorized a 3-year U.S. Metric Study, to determine the impact of increasing metric use on the U.S. This study was carried out by the National Bureau of Standards (NBS).
1971
The U.S. Metric Study resulted in a Report to the Congress: A Metric America, A Decision Whose Time Has Come. The 13-volume report concluded that the U.S. should, indeed, "go metric" deliberately and carefully through a coordinated national program, and establish a target date 10 years ahead, by which time the U.S. would be predominately metric.
The mole becomes SI's seventh base unit.
1973
The UCLA/USMA/LACES/STC and other professional groups National Metric Conference, the largest ever held, totaling 1700 registrants, took place at the University of California, Los Angeles in September. It took place as a result of USMA's recommendation. USMA coordinated and directed the event. One of the speakers was the U.S. Secretary of Commerce.
The American National Metric Council (ANMC) formed as a not-for-profit, non-advocative trade organization to plan and coordinate SI implementation by U.S. industry.
1974
The Education Amendments of 1974 (Public Law 92-380) encouraged educational agencies and institutions to prepare students to use the metric system of measurement as part of the regular educational program.
The initials "U.S." were added to the Metric Assocation name by the Board of Directors. The organization is now known as the "U.S. Metric Association, Inc." with the initialism "USMA".
1975
The Metric Conversion Act of 1975 (Public Law 94-168) passed by Congress. The Metric Act established the U.S. Metric Board to coordinate and plan the increasing use and voluntary conversion to the metric system. However, the Metric Act was devoid of any target dates for metric conversion.
1976
The National Council of Teachers of Mathematics (NCTM) started the National Metric Week tradition, with the first one during the week of 10 May 1976, the year after the Metric Conversion Act of 1975 was enacted.
1979
The Treasury Department's Bureau of Alcohol, Tobacco, and Firearms (BATF) requires wine producers and importers to switch to metric bottles in seven standard [liter and milliliter] sizes.
1980
The Treasury Department's Bureau of Alcohol, Tobacco, and Firearms (BATF) requires distilled spirits (hard liquor) bottles to conform to the volume of one of six standard metric [liter and milliliter] sizes.
1982
President Ronald Reagan disbanded the U.S. Metric Board and canceled its funding. Responsibility for metric coordination was transferred to the Office of Metric Programs in the Department of Commerce.
1988
The Omnibus Trade and Competitiveness Act of 1988 (Public Law 100-418) amended and strengthened the Metric Conversion Act of 1975, designating the metric system as the preferred measurement system, and requiring each federal agency to be metric by the end of fiscal year 1992.
1991
President George H. W. Bush signed Executive Order 12770, Metric Usage in Federal Government Programs directing all executive departments and federal agencies implement the use of the metric system. The Executive Order is also available as an appendix to: Interpretation of the SI for the United States and Federal Government Metric Conversion Policy
1994
The Fair Packaging and Labeling Act (FPLA) was amended to add a requirement for metric units on most consumer products.
1996 April 15
All four Canadian Stock Exchanges began decimal trading, the first exchanges in North American to abandon the old "pieces-of-eight" trading system and welcome the new decimal system. The old tradition of trading stocks in increments of one-eighth of a dollar, or 12.5 cents, dates back to when the Spanish mille dollar was divided into "pieces of eight".
1996 July
All surface temperature observations in National Weather Service METAR/TAF reports are now transmitted in degrees Celsius.
2000 September 30
Now suspended, the deadline for metricating highway construction, including all agreements, contracts, and plans processed by individual states for federally-funded highway construction to be in metric units, was canceled by Congressional action, leaving metric conversion as voluntary but still recommended to comply with the Omnibus Trade and Competitiveness Act of 1988.
2001 April 09
U.S. Stock Exchanges finalized the change to decimal trading. The Securities and Exchange Commission has ordered that all stocks must be quoted in dollars and cents rather than fractions by this date. The switch to decimal trading brought the U.S. in line with the rest of the world's major exchanges. This follows the change of the Canadian Stock Exchanges to decimal trading in 1996.
2004 July 08
UK Metric Association (UKMA) issued a comprehensive report, A Very British Mess, on the need to complete UK metrication.
2005 January 20
Speed limits in Ireland were converted from miles per hour to kilometers per hour (km/h). To accompany this, new cars have kilometers as the primary speed displayed on their speedometers. Wind speeds in weather reports were also changed to kilometers per hour. See the Irish Department of Transport announcement.
2007 January 08
"Metric Moon" press release: NASA has decided to use metric units for all operations on the lunar surface when it returns to the Moon. See the NASA announcement. NASA’s Constellation Program is to be metric, according to a Program Management Directive issued on 19 December 2007, with the metric system as the “primary system of measure” for the Constellation Program, Projects, Systems, and Mission.
2009 December 31
Now suspended indefinitely, the EU measurement directive that would have banned non-metric units in Europe (with limited exceptions, and with dual-labeling of products not permitted), has been canceled by the EU Commission, hoping in return that U.S. regulations will allow voluntary metric-only labeling on consumer products. The U.S. should allow metric-only packaging by amending the Fair Packaging and Labeling Act (FPLA). This would be a good response to the elimination of EU requirements for SI-only labels which had been plannned to take effect at the end of 2009.


See also USMA's list of Metric events and anniversaries
See also USMA's list of SI unit definitions


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