What’s a Kilogram? The Hunk of Metal That Defined It for 130 Years Has Been Retired
The closely guarded cylinder of platinum-iridium, kept under strict control in France, has outlived its usefulness
Once upon a time, a kilogram was defined by a hunk of metal stored beneath a trio of bell jars in a climate-controlled vault in the basement of the International Bureau of Weights and Measures in France.
The closely guarded cylinder of platinum-iridium was forged in 1889.
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