1. AN ARRANGEMENT FOR CONTROLLING THE SETTING OF A ROTARY STEPPING SWITCH AT A FIRST END OF A CONTROL LINE FROM A CONTROLLING SWITCH AT THE OTHER END OF SAID LINE; SAID ARRANGEMENT INCLUDING AT SAID FIRST END, A STEPPING MAGNET FOR ACTUATING SAID ROTARY SWITCH, AN INTERRUPTER CIRCUIT FOR SAID MAGNET, A TRANSISTOR AMPLIFIER FOR POWERING SAID INTERRUPTER CIRCUIT AND RECTIFIER MEANS THE OUTPUT OF WHICH IS CONNECTED TO THE INPUT OF SAID TRANSISTOR AMPLIFIER; SAID ARRANGEMENT FURTHER INCLUDING A RECTIFIER BRIDGE COMPRISING TWO PARALLEL-CONNECTED VOLTAGE DIVIDING NETWORKS EACH FORMING TWO ARMS OF SAID BRIDGE, A VOLTAGE SOURCE CONNECTED ACROSS SAID PARALLEL-CONNECTED NETWORKS, ONE OF SAID VOLTAGE DIVIDING NETWORKS INCLUDING A NUMBER OF RESISTANCES AT SAID FIRST END OF SAID LINE FOR VARYING THE RESISTANCE RATIO OF THE TWO ARMS OF SAID NETWORK UNDER THE CONTROL OF SAID ROTARY SWITCH, THE OTHER VOLTAGE DIVIDING NETWORK INCLUDING A NUMBER OF RESISTANCES AT SAID OTHER END OF SAID LINE FOR SELECTIVELY VARYING THE RESISTANCE RATIO OF THE TWO ARMS OF SAID OTHER NETWORK UNDER THE CONTROL OF SAID CONTROLLING SWITCH, AND THE INPUT OF SAID RECTIFIER MEANS BEING CONNECTED BETWEEN THE JUNCTION OF SAID TWO ARMS OF SAID ONE NETWORK AND THE JUNCTION OF SAID TWO ARMS OF SAID OTHER NETWORK, WHEREBY A DIFFERENCE BETWEEN SAID TWO RESISTANCE RATIOS EFFECTED BY A SETTING OF SAID CONTROLLING SWITCH CAUSES SAID STEPPING MAGNET TO ACTUATE SAID ROTARY SWITCH AND BALANCE SAID BRIDGE BY SELECTIVELY VARYING SAID SECOND MENTIONED RATIO.