Experts Suggest Replacing Definition of Kilogram

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The kilogram is the only one of the seven basic units of the international measurement system defined by a physical artifact rather than a natural phenomenon. International team of scientists suggest replacing the kilogram artifact -- a cylinder of platinum-iridium alloy about the size of a plum --with a definition based on one of two unchanging natural phenomena, either a quantity of light or the mass of a fixed number of atoms. They propose to adopt either one of two definitions for the kilogram by selecting a specific value for either the Planck constant or the Avogadro number.