|Before the advent of digital electronic voltmeters, accurate measurement of a voltage or impedance was achieved by applying the compensation method. The unknown quantity is compared with an adjustable known one of the same kind. The known quantity is changed until the difference is zero, which is detected by a sensitive null-indicator. In equilibrium, the unknown quantity is equal to the known one. In this way, voltages, currents and impedances can be accurately measured.
Presentation by Prof. Paul Regtien