Poggendorf compensation potentiometer

This principle is used every time one measures the electromotive force of an electrochemical cell. In this case the potential measuring device determines the difference between the electrochemical potentials of electrons in two pieces of the same metal, for example, in two copper wires. The classical device for doing this measurement is a Poggendorf compensation potentiometer but a modern in-... 

Fig. 9.2 Schematic diagram of a Poggendorf compensation potentiometer. The contact position C on slidewire AB is moved until no current flows in galvanometer G. Calibration of AB, for which position is related to voltage, permits determination of the EMF of cell X.

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