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Claim 1

A SIGNALLING ARRANGEMENT FOR A PUSHBUTTON TELEPHONE DIALLING SYSTEM COMPRISING CENTRAL OFFICE EQUIPMENT SERVING A PLURALITY OF TWO CONDUCTOR LINES, EACH HAVING A SUBSCRIBER STATION THEREON, VOLTAGE SUPPLY MEANS IN SAID CENTRAL OFFICE HAVING A POSITIVE VOLTAGE TERMINAL FOR SUPPLYING A POSITIVE VOLTAGE WITH RESPECT TO GROUND AND A NEGATIVE VOLTAGE TERMINAL FOR SUPPLYING NEGATIVE VOLTAGE WITH RESPECT TO GROUND, INTERROGATING MEANS IN SAID CENTRAL OFFICE NORMALLY CONNECTING SAID SUPPLY MEANS IN A FIRST INTERROGATING POSITION WITH SAID NEGATIVE TERMINAL CONNECTED TO THE FIRST OF SAID TWO CONDUCTORS AND SAID POSITIVE TERMINAL CONNECTED TO THE SECOND OF SAID TWO CONDUCTORS, A PLURALITY OF DIGIT SIGNALLING MEANS IN EACH OF SAID STATIONS SELECTIVELY OPERABLE TO MARK SAID CONDUCTORS IN DESIRED PERMUTATIONS AND COMBINATIONS, SAID PERMUTATIONS AND COMBINATION COMPRISING INDIVIDUALLY GROUNDING THE FIRST CONDUCTOR, INDIVIDUALLY GROUNDING THE SECOND CONDUCTOR, GROUNDING BOTH CONDUCTORS SIMULTANEOUSLY, GROUNDING NEITHER OF THE CONDUCTORS AND CONNECTING BOTH CONDUCTORS TOGETHER, EVACULATING MEANS IN SAID CENTRAL OFFICE MOUNTED BETWEEN EACH OF THE CONDUCTORS AND GROUND AND OPERATED RESPONSIVE TO SAID MARKINGS, AND REVERSE MEANS INCLUDED IN SAID INTERROGATING MEANS OPERATED RESPONSIVE TO THE OPERATION OF SAID EVALUATING MEANS TO CONNECT SAID SUPPLY MEANS IN A SECOND INTERROGATING POSITION WITH SAID POSITIVE TERMINAL CONNECTED TO SAID FIRST CONDUCTOR SAID NEGATIVE TERMINAL CONNECTED TO SAID SECOND CONDUCTOR THEREBY CHANGING THE MARKINGS OF SAID CONDUCTORS AND OPERATING SAID EVALUATING MEANS TO EVALUATE THE MARKED CONDUCTORS TO DETERMINE THE OPERATED DIGIT SIGNALLING MEANS.