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Some basic difficulties in the protection of telephone networks against dangerous overvoltage disturbances such as lightning are discussed, and a new method for measuring and recording such transients is presented. The method essentially consists of measuring the analog disturbance signals, converting and coding their temporal values into digital numbers easily available to shift register memories and subsequently recording the results either with a teleprinter for computer analysis and statistical abstracts or with a -recorder for a human observer. The instrument is capable of recording disturbance amplitudes of 0.1-MHz spectral content linearly with an 300-V interval up to voltages of 5 kV, the sampling rate of the A/D converter used for the recording being adjustable to values of 500 kHz, 1 MHz or 2 MHz. The digital circuits of the instrument use positive logic and are realized for the most part by TTL and MOS technologies.