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Recipe for a Kilogram

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Science  08 May 1998:
Vol. 280, Issue 5365, pp. 823-824
DOI: 10.1126/science.280.5365.823

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Physicists are closing in on an absolute standard for the kilogram, the one fundamental unit still tied to an artifact, namely, a hunk of platinum-iridium that is locked in a safe in France. One group is attempting to establish a standard by counting the atoms in a known mass of silicon; the other is trying to find a way to reliably manufacture an electromagnetic force that exactly balances the force of gravity on a kilogram. Ideally, physicists would like to have both methods work, so that they could have a new kilogram as well as something to double-check it against.