the present system is not easily scalable. The smaller the scale, the larger the uncertainty in measurement because a very long sequence of comparisons is necessary to get from a 1 kg standard down to tiny metal mass standards in the milligram (mg) range, and each comparison entails an added uncertainty. As a result, although a 1 kg artifact can be measured against a 1 kg standard to an uncertainty of a few parts in a billion, a milligram measured against the same 1 kg has relative uncertainties of a few parts in ten thousand. That is not satisfactory for the ever more demanding needs of modern metrology, device manufacture, material science, pharmaceutical research and testing, and environmental monitoring , to name only a few. Increasingly, those endeavors require accurate measurements on the order of micrograms (millionths of a gram, or 10-6 g) and smaller. nist.gov/pml/si-redef/kg_intro.cfm
Posted on: Sat, 22 Nov 2014 10:37:52 +0000
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