Even physical characteristics of things you wouldn’t think would change over just a relatively short time. But that’s what’s happening to the object that has served as our definition of the kilogram. That object is a cylinder of platinum and iridium that was cast 118 years ago. Unfortunately if you have an insistence on the utmost accuracy that cylinder has lost approximately 50 micrograms of mass since its creation. Science Daily notes the problem here and a proposed solution.
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