On a wooden base is mounted a metal slide with a wooden handle, hinged at one end so that the opposite end can touch one of the 10 metal buttons arranged in an arc; the first is marked with a zero, the following buttons with numbers from 1 to 9, the last with zero. Insulated wires are connected to the buttons which allowed contact with the resistances of the rheostat itself; by moving the switch it was possible to insert a variable resistor into the circuit.

Device on display.