19. THE COMBINATION WITH A BYTE CONVERTER FOR RECEIVING INPUT BYTES CONSISTING OF ONE NUMBER OF BITS AND TRANSMITTING OUTPUT BYTES CONSISTING OF A DIFFERENT NUMBER OF BITS, OF A CHECK CIRCUIT COMPRISING MEANS FOR PROVIDING AN INPUT EVEN PARITY CHECK-BIT FOR EACH INPUT BYTE, AN EVEN PARITY CHECK-BIT FOR EACH OUTPUT BYTE, COUNTER MEANS EVEN PARITY CHECK-BIT FOR EACH OUTPUT BYTE, COUNTER MEANS FOR RECEIVING SAID INPUT AND OUTPUT CHECK-BITES, MEANS FOR SAMPLING SAID COUNTER MEANS ONLY WHEN A GROUP OF INPUT CHECK-BITS AND A GROUP OF OUTPUT CHECK-BITS BOTH RELATE TO THE SAME SELECTED SUCCESSIVE BITS, AND MEANS RESPONSIVE TO SAID COUNTER MEANS FOR PROVIDING AN ERROR INDICATION WHEN THE COUNT IS ODD.