In a world of incessant change, some things have to stay the same. One is the set of values for the fundamental physical constants—such as the speed of light or the charge of the electron—that underlie precision measurements in industry, science, and medicine worldwide.

Yet even the constants themselves occasionally change incrementally to reflect the latest experimental determinations. The values are determined and issued by the Task Group on Fundamental Constants of the International Council for Science’s Committee on Data for Science and Technology (CODATA), of which the United States is one of 23 member nations. CODATA collects the best determinations from academic laboratories, independent standards laboratories, and national metrology institutes. By international agreement, a new set of official suggested values is published every four years, and NIST is now displaying the most recent (the 2014 values, published two months ago) on its website.

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