Book Reviews
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Wednesday, May 28, 2003
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The Changing Definition Of Kilogram: "The NYTimes is reporting that the platinum-iridium standard mass for the kilogram is shedding at an appreciable rate -- at least compared to other reference masses. The Pt-Ir cylinder is kept in France, and measured annually, and the slight discrepancy is important because the kg is an SI base unit -- thus other quantities such as the Volt are based on it. A new standard is being sought -- the two frontrunners are counting the number of atoms in a perfectly spherical single crystal of silicon, and another technique uses a device known as the Watt balance." [Slashdot]
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