A primer on electrical units in the Système International

I examine the dissemination of the electrical units, from basic physical laws to commercial calibrations. I discuss the important distinction between realization and representation of units, which refers back to the distinction between SI (Le Système International d’Unités) units and practical units. I then outline the current dissemination of electrical units, heavily based on the fundamental quantum standards (Josephson voltage and quantized Hall resistance standards), as well as on a classic metrology experiment, the calculable capacitor. We will see that this chain of unit realizations is one way physicists test the accuracy of the basic physical laws. As an example of the dissemination, I also outline the transfer chain from the primary voltage standard to the factory floor. Finally, I briefly discuss some areas of current research which have the potential to induce permanent changes in the definition of SI units (in particular the kilogram), and to close the “metrology triangle.”