A dia sweeping brush contact, one for the main central contact and other for individual resisters, made from hardened copper phosphor bronze strips inforced by a spring strip are held in place by a rotating bakelite knob. The values of resisters are engraved on the vulcanite plate indicated by the index on the edge of knob at each click stop. Constantan wire, double wound resisters are dipped in boiling wax for constant values. Accuracy 0.1 % Ten steps of 0.1 ohm total 1 ohm, or Ten steps of 1 ohm total 10 ohms.