The revised International System of Units (SI), expected to be approved late in 2018, has implications for physics pedagogy. The ampere definition, which dates from 1948, will be replaced by a definition that fixes the numerical value of the elementary charge e in coulombs. The kilogram definition, which dates from 1889, will be replaced by a definition that fixes the numerical value of the Planck constant h in joule seconds. Existing SI equations will be completely unaffected. However, there will be a largely negligible, but nevertheless necessary, change to published numerical factors relating SI electrical units to their corresponding units in the Gaussian and other CGS systems of units. The implications of the revised SI for electrical metrology are neatly illustrated by considering the interpretation of results obtained from a current balance in the present SI and in the revised SI.

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Prior to 1983, when the meter per second was defined independently of c, the speed of light could be measured. The venerable history of such measurements ended in 1983. Similarly, a measurement of ΔνCs in hertz became a logical impossibility as of 1967. It will also become meaningless to measure h and e in SI units (as well as the Boltzmann and Avogadro constants, which do not concern us here) after the revised SI is implemented.

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