U.S. National Institute of Standards and Technology

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Inaccurate laboratory measurements can mean wrong medical diagnosis and treatment, lost production time, wasted energy and materials, manufacturing rejects, and product liability. The U.S. National Institute of Standards and Technology and national standards laboratories around the world distribute Standard Reference Materials, such as metals, chemicals, rubber, plastics, engineering materials, radioactive substances, and environmental and clinical standards that can be used to test the accuracy of analytical procedures.1... 

Accuracy and Interpretation of Measured pH Values. To define the pH scale and pertnil the calibration of pH measurement systems, a scries of reference buffer solutions have been certified hy the U.S. National Institute of Standards and Technology iNIST). The acidity function which is the experimental basis for the assignment of pH. is reproducible within about O.IKl.I pH unit from It) to 40T. However, errors in the standard potential of the cell, in the composition of the buffer materials, and in the preparation of the solutions may raise the uncertainty to 0 005 pH unit. The accuracy of ihe practical scale may he furthei reduced to (I.Ot)X-(l.(ll pH unit as a result of variations in the liquid-junction potential. 

The standard kilogram is defined as the mass of a cylindrical bar of platinum-iridium alloy stored in a vault in a suburb of Paris, France. There are 40 copies of this bar distributed throughout the world, with two (Numbers 4 and 20) stored at the U.S. National Institute of Standards and Technology near Washington, D.C. 

Certified reference material (CRM) A reference material, accompanied by a certificate, one or more whose property values are certified by a procedure that established its traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence. For example, standard reference materials from the U.S. National Institute of Standards and Technology (http //www.nist.gov) are considered CRMs. 

The U.S. National Institute of Standards and Technology defines the calorie as joules. 

JFL thanks the U.S. National Institute of Standards and Technology for partial support of his thermochemical studies. JAMS thanks the PRAXIS XXI Program (PRAXIS/2/2. l/QUI/51/94), Portugal, for financial support. The authors also thank Drs Dunbar, Ho and Zavitsas for sharing with us unpublished data and insights. 

The U.S. National Institutes of Standards and Technology provides absolute calibration of such detectors see, for example, R.W. Leonhardt and T.R. Scott, Deep UV excimer laser measurements at NIST, Proc. SPIE 2439, 448 459 (1995). 

AMS measures the ratio of all to total carbon in the sample, which is then compared to the same ratio from an external standard prepared and measured in identical circumstances. The most commonly used external standard is SRM-4990-C, oxalic acid reference standard from the U.S. National Institute of Standards and Technology (NIST) at a raw isotope ratio of 1.1361 Modern with a content of 1.106%. Other international standards are available from the International Atomic Energy Agency (Vienna). The Center for AMS at Lawrence Livermore National Laboratory (Livermore, California) has generated secondary standards of oxalic acid at 12 and 100 Modern. 

Scientists at the U.S. National Institute of Standards and Technology measured a force of 174 yN exerted by a weak electric field on a vibrating crystal of 60 Be ions cooled to 0.5 mK in an electromagnetic trap. (M. J. Biercuk et al., arXiv.org 1004.0780v3 [quant-ph] 24 Apr 2010.)... 

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