A time encoding system with an associated dial-shaped setting mechanism is presented, which allows automatic changes in tariff rates to occur at half hourly intervals if required at a telephone exchange. The rates charged are dependent on a clock rate which is fixed by the distance being called and by the device described, one of which is associated at the exchange with each distance dependent clock generator. A control timing unit produces a pulse accurately every half hour, and an electronic encoder accumulates this information in 48 bits in a very redundant but reliable code, so that each half hour module is identifiable at a coded output. This in turn drives a dial shaped device which allows various set points to be chosen at which changes can be made.
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