ELECTRONIC INSTRUMENTS-NAMELY, LEVEL-MEASURING INSTRUMENTS,NOISE-MEASURING INSTRUMENTS, DISTORTION-MEASURING INSTRUMENTS FOR MULTICHANNEL RADIO LINKS AND WIRED COMMUNICATION LINES, MEASURING INSTRUMENTS FOR PCM TRANSMISSION, REFLECTION-FACTOR-MEASURING INSTRUMENTS, PHASE-MEASURING INSTRUMENTS, FREQUENCY COUNTERS, NOISE ANALYZERS, ATTENUATORS, AND EQUALIZING NETWORKS FOR INFORMATION TRANSMISSION AND MONITORING AND RECORDING INSTRUMENTS FOR SUCH MEASUREMENTS