The DF 64 Error Ratio Measuring Set is used for measuring and recording bit and block error ratios on analog and digital data communications equipments. As the DF 64 is an universal instrument it can be used for testing the PCM-30 D data transmission system of the Bundespost. This involves measurements on PCM multiplexers with interfaces conforming to CCITT rec. G.703 and measurements of modems with interfaces conforming to CCITT rec. V.11. When used as an external error counter, the DF 64 can be used to record the bit errors of applied external signals up to 2 Mbit/s. This is possible with any type of communications equipment.