SEVRES, France – The kilogram is undergoing an update.

No, your bathroom scale will not suddenly become nicer and a kilo of fruit will always weigh a kilo. But the way scientists define the exact mass of the kilogram is about to change.

Until now, his mass was defined by the grandfather of all the kilos: a metal cylinder the size of a golf ball locked in a vault in France. For more than a century, it's the only real kilo that everyone else was based on.

Not anymore.

Meeting at Versailles, west of Paris, governments are expected to endorse on Friday the plan to instead use a scientific formulation to define the exact mass of a kilo. The change should have practical applications in industries and sciences that require ultra-precise mass measurements.

The Grand K: And that will mean the redundancy for the so-called Grand K, the kilo that has surpassed them all since 1889.

Made from a corrosion resistant alloy of 90% platinum and 10% iridium, the international kilo prototype has rarely emerged. Yet, its role has been crucial as the foundation of the globally accepted system of measuring the mass upon which international trade depends, for example.

Three different keys, kept in separate locations, are needed to unlock the safe where the Grand K and six official copies, known collectively as "The Heir and Spare Parts" – are buried together under Glass ringtones at the International Bureau of Weight Lifting. Measures, in Sèvres, in the western suburbs of Paris.

Founded by 17 nations in 1875 and known by its French initials, the BIPM is the guardian of the seven main units used by humanity to measure its world: the meter for the length, the kilogram for the mass, the second for the time, the ampere for the electric current, the kelvin for the temperature, the mole for the quantity of a substance and the candela for the luminous intensity.

Of the seven, the kilo is the last one that still relies on a physical artifact, the Grand K. The meter, for example, was previously a metal bar one meter long, but is now defined as the length for which light travels in the vacuum 1/299 792 458 of a second.

"This is, if you will, a festive moment, as it is like the last standard of 1875 that will eventually be replaced by a new innovation," said Martin Milton, director of the BIPM, in an interview with The Associated Press. "Everything else has been recycled, replaced and improved. This is the last improvement that goes back to the initial conception of 1875. This is a tribute to what was done in 1875, and it lasted so long. "

It is only very rarely and with great caution that the BIPM's master kilograms have been carefully removed, so that the other kilograms returned to Sevres from around the world can be compared to these, to be sure they were always correctly calibrated. a particle of dust or two.

America too: Although many Americans generally think that the weight is in pounds and ounces, the United States is officially a country of the kilo: it is one of the 17 founders of the BIPM who founded the BIPM in 1875. The kilo the United States is called K20 and was allocated to the country in 1889 by the BIPM, with another, K4. One kilo equals 2.2 pounds.

The United States also has another six kilograms of platinum iridium: the K79, 85, 92, 102, 104 and 105. They are all monitored by the National Institute of Standards and Technology, a branch of the US Department of Commerce. United States.

To check their mass, K20 and other kilograms from about three dozen other countries were measured in Sevres against the main kilograms of the BIPM in a laborious calibration exercise from 1988 to 1992. The K20 was measured again at the BIPM in 2014.

Even as humans talked, fought and slaughtered by tens of millions in the 20th century, they shared the kilo. The kilo allocated to China in 1983, when it began to adopt market reforms that made it an economic monster, was the first manufactured with very high precision diamond machining. Awarded to Japan in 1894, K39 was later ceded to South Korea in 1958.

The kilo is "a tribute to man's ability to collaborate," says Milton. "It's called a great work of peace, in fact, because it's one of the areas where all the states in the world come together with the same goal."

The new definition: The kilo of metal is being replaced by a definition based on Planck's constant, which is part of one of the most famous equations of physics, but which is also extremely difficult to explain. Suffice it to say that the update should ultimately prevent countries from occasionally returning their kilos to Sevres to be calibrated against the Grand K. Scientists should instead be able to accurately calculate an exact kilogram without having to measure a precious block of metal against another.

Milton says the change will have applications in the computer, manufacturing, pharmaceuticals, climate change study and other sciences in which precise measurements are needed.

"The system will be intrinsically correct by referring to the laws of science, the laws of nature," he said. "We will not have to just assume that a particular object never changes."

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