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The Importance of Unified Measurements
In the deep basement of a building in suburban France,
there is a small cylinder 39.17 mm in diameter and height.
The 120-year standard
In the 18th century, countries and regions used different weights and measures.
France alone used about 800 different units.
Inaccurate measurements caused confusions in communication, trade, and administration.
Accurate and unified standards needed for breaking down the chaos!
In France, in 1791, the scholars of Academy of Sciences defined
1 mm as one-twenty millionth of the meridian
and 1 kg as the weight of 1 ℓ of water at 4℃ when water density was the highest.
Length was also important for measuring the volume of 1 ℓ.
For six years since 1792,
Delambre and Mechain measured the length of the meridian.
Then created was a one-meter bar and a one-kilogram weight.
The standard prototypes of length and mass
However, errors were found.
Due to the miscalculation of the Earth's oval,
meter prototype came 0.2 mm short of one-twenty millionth of the meridian.
Duplicates of meter bars had differences of one-ten thousandth meter.
The density of water was the highest at 3.984℃, not 4℃
and the mass of kilogram prototype was inaccurate.
"If we want absolute standards of length, time, and mass,
we can't find them in Earth."
- James Clerk Maxwell (1831 - 1879), Physicist
In 1983, the meter was defined as
the length that light travels in a vacuum for 1/299,792,485 of a second.
Time (s), electric current (A), and temperature (K)
were defined based on the invariables of the natural phenomena.
However, the mass (kg) was
based on the kilogram prototype made 120 years ago.
In the measurement science, kilogram is like a stain on a white jacket.
and slight differences between the mass prototype and duplicates.
In the basement of International Bureau of Weights and Measures,
there is a treasure, or a troublemaker,
that has been the standard of all masses for 120 years.
At the 24th General Conference on Weights and Measures in 2011,
the kilogram will be redefined, hopefully.