April 7, 1795 by law the metric system is established in France.

On this day (April 7), 1795, the metric system is established by law in France.
Since ancient times, measures have been necessary; measures to build, measures to cook, measures to make clothes...
The measurements were taken with parts of the human body; feet, hands, elbows, arms, thumbs,... This caused a problem when exchanging measurements since each one has a different body measurement.
Little by little they tried to take more "unified" measures; pitchers, arrobas, fanegas (for liquid), leagues, varas (for distances), pounds (for weight)... although there was still confusion between territories.
Just after the French revolution, they wanted to suppress everything that meant the old regime and replace it with one more identified with rationalism. For this reason, a commission of scholars (including Lavoisier, Lagrange, Laplace, among others) studied this change in the metric system.
The commission's work resulted in different measures;

Meter

To obtain the meter they took the distance between the north pole and the equator. That distance was divided into 10 million parts. That "part" is "one meter".
From the subway, his "companions" appeared;
Each subdivision in ten of the meter is "the decimeter"
Each subdivision of ten of the decimeter is "the centimeter"

Liter

they took a Cube that was 10 centimeters on each side and all that fits in that cube of liquid is one liter.

Kilo

All that the water weighs inside the 10 centimeter cube (a liter of water) is a kilo
This decimal metric system was adopted in France and then, little by little, it was adopted in the rest of the world.
In Spain it was officially adopted in 1849
In Great Britain it was officially adopted in 2000
As a curiosity, there are currently only 3 countries that do not officially use the metric system; Liberia, Myanmar, and the United States.
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- Mr. Director, I have already measured the soccer field
- and how tall is it?
- 565 feet long
- how?
- 565 feet long
- ok, and in meters?
- don't know
- well I don't understand it
- do the conversion
- let's see... I get 172 meters... 172!... it can't be
- what feet have you turned into?
- well in the Anglo-Saxon "feet" which are 1 "foot" equal to about 0.3 meters
- oh, no
- right?
- that is the Anglo-Saxon "foot" but I have measured with my foot.
- this is chaos!