994,266. Automatic exchange systems. SIEMENS & HALSKE A.G. March 9, 1962 [March 10, 1961], No. 9094/62. Heading H4K. In an exchange having a plurality of channels and circuit means for storing information indicative of the or each subscriber operatively connected to a channel, the circuit means controlling the connection of the or each subscriber to the channel, the exchange traffic is measured by monitoring this stored information. In the time division system shown in Fig. 1, speech connections between subscribers Tn1, Tnx are established over the multiplex highway SM by cyclically closing gates S1, Sx which are closed by pulses stored in circulating stores Ua (for the calling subscriber) and Ub (for the called subscriber) these stores comprising combinations of delay lines there being one combination for each subscriber. For performing a busy test an address register G is provided with the wanted subscriber's address and this feeds comparators Va, Vb whose other inputs are taken from the stores Ua, Ub. If the wanted subscriber is busy, then at some time during the pulse cycle one of the comparators provides a signal to the control circuit E which may then insert a pulse at the calling subscriber's phase into Ud. This opens gate gb to feed busy tone in this pulse position to the highway SM and thence to the calling subscriber. To determine the average number of channels in use a gate SV1 is opened for one cycle every 36 seconds and the number of pulses received from Ua or Ub are counted at Z1. The gate SV1 may instead be opened at a phase corresponding to the last available channel, thereby giving an indication of the duration in which there is danger of a call being lost through lack of an available channel. Alternatively the gate may be opened at some other phase to indicate the extent to which a particular channel is occupied. To determine the number of times a call has been unsuccessful the number of insertions of a pulse into Ud may be measured by counter Z2. To establish how often a call is made to a busy subscriber a counter Z3 is pulsed when an engaged tone order is inserted in Ud, but only if a comparator Va or Vb is also providing an output at this time. Congestion, i.e. occupancy of all pulse channels, may be measured by feeding the outputs from Ua and Ub to a counting arrangement Z4 comprising two meters the first of which is stepped by the pulses received, and which is reset every cycle. Every time a full count is obtained a second meter is stepped. The total number of calls attempted by calling subscribers may be measured, by counting on Z5 the number of addresses inserted in Ua by the control circuit E. To count the number of calls attempted to wanted subscribers, the register MM which receives the digits from the calling subscriber is arranged to emit a pulse to Z6 every time the final digit of such a number is inserted into Ub. If the system is such that an insertion occurs whether the subscriber is busy or not then Z6 may be stepped backwards to cancel this recording by the output from the comparators Va or Vb. Arrangements for measuring the number of completed calls may be provided in which a store like Ud is provided for the emission of a calling signal and monitoring the control signals sent from E to cause deletion of pulses therein consequent upon the called subscriber's reply. To determine how long a particular subscriber uses his telephone either as a calling or a called party, the subscriber's identity is entered into GZ and a comparator VZ emits a pulse to a counter Z7 every time that identity is emitted from Ua or Ub. Arrangements for measuring interexchange traffic are shown in Fig. 2. Each exchange F1, F2 . . . has associated speech highways SM1, SM2 . . . leading to a central switching circuit in which gates such as k1a, k2a controlled by circulating store UZ can be cyclically pulsed to interconnect exchanges such as F1, F2 for that pulse position. This pulse position is also recorded in a subscriber's store such as U in the exchange. Pulse positions derived from U of F1 are fed to a counter Z1e via a gate Z1e which is opened by a comparator device V only if store UZ contains the identities of contacts such as k1a, k1b capable of effecting connection between exchange F1 and one of the other exchanges. This gives the total inter-exchange traffic involving F1. Counter Z12e indicates the traffic between F1 and F2, gate S12e being opened only when UZ stores the identities of pairs of gates such as kla, k2a and similarly for traffic F1 and the other exchanges. The output V from UZ may be fed to similar equipments in the other exchanges.