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A chronology of the SI metric system 

Important dates in the history of the modern metric system:

Authorities give credit for originating the metric system to Gabriel Mouton, a French vicar, on about this date
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.
The U.S. Mint was formed to produce the world's first decimal currency (the U.S. dollar consisting of 100 cents).
France officially adopted the metric system.
Napoleon temporarily suspended the compulsory provisions of the 1795 metric system adoption.
The metric system reinstated as the compulsory system in France.
The use of the metric system made legal (but not mandatory) in the United States by the Metric Act of 1866 (Public Law 39-183). [See: and:] This law also made it unlawful to refuse to trade or deal in metric quantities.
Treaty of the Metre signed in Paris by 18 nations, including the United States. The Treaty 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.
As a result of the Treaty of the Metre, the U.S. received a prototype meter and kilogram to be used as measurement standards.
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.
The Metric Association formed as a non-profit organization advocating adoption of the metric system in U.S. commerce and education. The organizational name was later changed to the U.S. Metric Association (USMA).
The International System of Units began its development at the 10th CGPM. Six of the new metric base units were adopted.
The meter was redefined in terms of wavelengths of light by the 11th CGPM, and the new metric system was given the official symbol SI for the Système International d'Unités , the "modernized metric system".
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."
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).
The U.S. Metric Study resulted in a Report to the Congress: A Metric America, A Decision Whose Time Has Come . The 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 UCLA/USMA/LACES/STC/and other professional groups National Metric Conference , the largest ever held with 1700 registrants, took place in Los Angeles in September.
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.
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 Metric Conversion Act of 1975 (Public Law 94-168) passed by Congress. The Act established the U.S. Metric Board to coordinate and plan the increasing use and voluntary conversion to the metric system. However, the Act was devoid of any target dates for metric conversion.
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.
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.
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.
The meter is redefined in terms of the speed of light by the 17th CGPM, resulting in better precision but keeping its length the same.
The Omnibus Trade and Competitiveness Act of 1988 amended and strengthened the Metric Conversion Act of 1975, designating the SI metric system as the preferred measurement system, and requiring each federal agency to be metric by the end of fiscal year 1992.
President George 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 Fair Packaging and Labeling Act (FPLA) was amended by the Food and Drug and Administration (FDA) to require the use of dual units (inch-pound AND metric) on all consumer products.
All four Canadian Stock Exchanges began decimal trading on April 15, the first exchanges in North American to abandon the old "peices-of-eight" trading system and selcome 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".

Future metric deadlines:

1999 December 31
All products sold in Europe (with limited exceptions) will be required to have only SI metric units on their labels. Dual labeling will not be permitted. The EU Commission voted to extend the deadline for implementation of the labeling directive for 10 years, giving more time for companies to comply and for U.S. regulations to allow metric-only labeling on consumer products. New deadline: 2009 December 31. See Did You Know That for more details on this topic.
2000 September 30
All agreements, contracts, and plans processed by individual states for federally-funded highway construction must be in metric units. This deadline has been canceled by recent Congressional action, leaving metric conversion as voluntary but still recommended to comply with the Omnibus Trade and Competitiveness Act of 1988 . The vast majority of the State Departments of Transportation are using the metric system now, and they plan to continue despite the deadline being rescinded.
year 2000 or soon after
U.S. Stock Exchanges change to decimal trading. As an intermediate step toward that goal, stock prices are now quoted in sixteenths, or 6.25 cent increments, down from eighths, or 12.5 cents. The switch to decimal trading will bring the U.S. in line with the rest of the world's major exchanges. This follows the change of the Canadian Stock Exchange to decimal trading in 1996.

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Updated: 1999 June 25