801,295. Code telegraphy. REUMERMAN, T., and HELMIG, W. H. T. April 27, 1956 [May 10, 1955 ; July, 20, 1955], Nos. 13519/55 and 21017/55. Class 40 (3). [Also in Groups XIX and XXXVIII] Relates to system for the transmission of data by means of symbol groups comprising letters, digits, &c. of the type in which each symbol group is transmitted together with a corresponding check symbol determined by applying a predetermined arithmetical rule to the symbols comprising a group. At the receiving end the check symbol of the received symbol group is determined and compared with the transmitted check symbol and if the two check symbols do not correspond a warning signal is sent to the input end and the incorrectly received symbol group is re-transmitted. Where the symbols are letters they are given corresponding numerical values in order to compute the check symbols. Examples of arithmetically consistent and arithmetically non-consistent number checking systems are given in the Specification. In the case of arithmetically consistent systems numbers fed into, for example a computer, may be subjected to various arithmetical operations and the result fed into an output register. If the same arithmetical operations are also performed upon the check symbols of the numbers fed into the machine, the check symbol of the result will also appear in the output register. The system includes input storage means which may be in the form of punched or magnetic tape, punched cards, a mechanical or electrical register, or a magnetic or electric storage device. Fig. 1 shows a device for recording the symbol groups to be transmitted, together with their check signals, on a punched tape. The symbols selected by a keyboard 1; are transferred via conductor 3 to the punching device 4, and simultaneously are supplied to a check symbol computer 5 which determines a check symbol - for each group. At the end of a symbol group, depression of space-bar 2 operates switch control device 6 and causes switch 7 to operate through a complete sequence. In the initial position of switch 7 shown, an unblocking device 8 is energized to keep the keyboard 1 unblocked which may be indicated by a lamp 13. As .soon as switch 7 leaves its first contact, the keyboard is blocked and in its second position switch 7 energizes a read-out device 9 which transfers the check symbol from the computer 5 to the punching device 4, whereby the check symbol is punched in the tape. In its third position, switch 7 energizes the punching device via line 10 so that a space symbol is punched in the tape after the check symbol, and in its fourth position switch 7 energizes line 11 whereby the punch is reset and a device 12 resets the computer. When switch 7 returns to its initial position the keyboard is unblocked ready for the insertion of the next symbol group. The prepared tape is fed to a tape reader 14, Fig. 2, to cause an impulse transmitter 16 to transmit impulses corresponding to the symbols on the tape to a transmission line 17 leading to the remote receiving station. The symbols recorded on the tape are also supplied to a storing device 18, which stores all the symbols of a group, and to a space symbol detector 19 which is operated by a space symbol to energize a blocking device 20 to stop the tape reader 14. At the receiver Fig. 3, the received symbols of a group are stored in a device 31 and are also supplied to a check symbol computer 32, which determines the check symbol of the symbol group and compares it with the received check symbol. A space symbol detector 33 is operated by the space symbol and energizes a read-out device 34 which supplies a voltage to line 35 if the received symbol group is correct, and to line 36 if it is incorrect. Energization of line 35 operates a " right symbol " generator 37, which transmits a signal to the transmitter over line 21, and operates a read-out device 38 controlling a printing mechanism. The voltage on line 36 operates a " wrong symbol " generator 39, which transmits a corresponding signal over line 21, and operates a device 40 which resets the storing device 31. Both " right " and " wrong " signals are passed through a device 41 which via 42 resets the computer 32. At the transmitter, the signal over line 21 is applied to a detector 22 which energizes a line 23 if the symbol group is wrong, and a line 25 if it is correct. Energization of line 23 operates a read-out device 24, whereby the symbol group stored in device 18 is supplied to impulse transmitter 16 and re-transmitted, and also operates a counter 28 which when it has been operated a predetermined number of times operates an alarm 29, or may switch over to a standby device. If line 25 is energized a device 26 resets the storing device 18, and a device 27 unblocks tape reader 14 to allow transmission of the next symbol group. To prevent the system coming to a standstill in the event of distortion of the space symbol during transmission, a space symbol generator may be provided at the transmitter which emits a space symbol at regular intervals and is connected to line 17 a predetermined time after the operation of the space symbol detector 19 and disconnected as soon as a signal appears on line 21. The Specification gives details of a circuit for a five-element telegraph code transmission system, Figs. 6, 7, 8 (not shown), and describes a calculating device, and a system for transmitting meter readings (see Group XXXVIII).