This one looks more complex than you describe. However, I have one of the more simplified units, as you describe (At least, I think I do), which I would like to learn more about... Dan On 8/24/2012 8:00 AM, volt-nuts-request@febo.com wrote: > Its a potentiometer used to measure dc voltage. > A standard cell was used to set the total voltage across a series string > of resistors and a slide wire. > The dc voltage to be measured was balanced against the voltage developed > across a selected substring of resistors and the tap on a slide wire. > Lead acid batteries and similar cells were used as a source for the > slide wire and series resistor string current. > A galvanometer was used a s a null detector to determine when the > v0oltage across the slide wire and series resistor string were equal. > The resistors were typically immersed in mineral oil contained within a > copper tank below the ebonite (or similar ) faceplate. > > Bruce