Maker's Name: 
Otto Wolff, Berlin
Where made: 
51 × 32 × 23 cm

Mahogany case has ebonite plate carrying heavy brass contacts and switches with ebonite handles. Inside the case are resistance coils, calibrated at 20C.

Such potentiometers were used to measure voltages by comparison using a battery as energy source, a standard cell as voltage reference, and a galvanometer . The galvanometer was connected between the point of unknown potential and one terminal of the potentiometer. When the two are at the same potential, no current flows. The voltage at the potentiometer terminal can be varied in a controlled way by switching in combinations of resistance coils. A similar measurement with a standard cell of accurately known voltage calibrates the result. At "balance" no current was drawn from the circuit under test, which is a great advantage, but , although the method is very accurate, it was rather slow.