On the application of zener diodes to expanded scale instruments
A. J. Corson · Transactions of the American Institute of Electrical Engineers Part I Communication and Electronics · 1958
With the advent of closer regulation of industrial electric circuits comes the need for high-accuracy limited-range measurement about a mean value, representative of normal circuit conditions. This applies with particular force to voltage and frequency measurement, and there are many instances in which it is equally true in the measurement of current and power.