Change for a Unit Humanity Uses to Measure Its World

The kilogram is getting an update
By Newser Editors and Wire Services
Posted Nov 14, 2018 2:38 PM CST

(Newser) – The kilogram is getting an update. No, your bathroom scales won't suddenly become kinder and a kilo of fruit will still weigh a kilo. But the way scientists define the exact mass of a kilogram is about to change. Until now, its mass has been defined by the granddaddy of all kilos: a golf ball-sized metal cylinder locked in a vault in France. For more than a century, it has been the one true kilogram upon which all others were based. No longer. Gathering in Versailles, west of Paris, governments are expected on Friday to approve plans to instead use a scientific formulation to define the exact mass of a kilo. The change is expected to have practical applications in industries and sciences that require ultra-precise measurements of mass. An in-depth explainer from the AP:

  • The move will mean redundancy for the so-called Grand K, the kilo that has towered above them all since 1889. Made of a corrosion-resistant alloy of 90% platinum and 10% iridium, the international prototype kilo has rarely seen the light of day. Three different keys, kept in separate locations, are required to unlock the vault where the Grand K and six official copies—collectively known as "the heir and the spares"—are entombed together under glass bell-jars at the International Bureau of Weights and Measures, in Sevres on the western outskirts of Paris.

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