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A few facts about the metric system

During the French Revolution, many people in France realized that their numerous local measures and weights systems of measurement were archaic, needed to be changed and - ideally - unified. That's exactly what Charles Maurice de Talleyrand wanted to implement: a radical change in regard to the way units were to be measured.

In 1790, he proposed to the French National Assembly the development of a new system. Other nations were also asked to co-operate. Great Britain did not want anything to do with the creation of a new system of measurement though.

In 1791, the French Academy of Sciences decided to set up a commission and one of its implementations was the standardized definition of length based on the size of the Earth. Length would now be defined via the metre, which would be equal to 1/10 000 000 of the length of the meridian arc from the equator to the north pole.

The metric system follows a pattern that is decimal.

Units can easily be divided or multiplied
by an integer power of ten. For example:

1/10 of a metre is a decimetre
(0.1 metre)
1/100 of a metre is a centimetre
(0.01 metre) 
cent" in French means hundred)]

1/1000 of a metre is a millimetre
(0.001 metre)
mille" in French means thousand].

The hectometre is 100 metres and
the kilometer is 1000 metres.

The International System of Units (SI) now includes seven base units or, if you prefer, physical constants.

The metre (length), the kilogram (mass), the ampere (electric current), the mole (amount of substance), kelvin (temperature), candela (light intensity) and the second (time).

SI is always adapting to new technologies
and the need to be as precise as possible.

Hence, in the SI, the metre is defined as
1 / 299 792 458 of the distance light can travel in one second. As for the kilogram, initially defined as the mass of one cubic decimetre of water at 4 degrees Celsius, it is now defined by SI via the Planck constant.

In 1975, the United States' Metric Conversion Act did declare that the metric system was the preferable system for weights and measures but it did not suspend the use of other units in the country.

As of today, the United States does not use the metric system on a wide scale.

For more information on the metric system

Britannica. Metric system.

Bureau International des Poids et Mesures.
The International System of Units (SI).

Wikipedia. Metric system.

Fun fact
Robert Radford (Quebec, Canada) © MMXXIII