Measuring apparatus and instruments, namely, apparatus and instruments for measuring of digital frequencies, radiation measuring apparatus and instruments; electronic ultrasonic test equipment, namely, ultrasonic wave receivers, ultrasonic wave analyzers, frequency analyzers, sound filters, frequency filters, ultrasonic wave filters, sound amplifiers, ultrasonic wave amplifiers, frequency amplifiers, sound meters, ultrasonic wave meters and frequency meters, ultrasonic flaw detectors, thickne...