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ELECTRICAL AND ELECTRONIC INSTRUMENTS AND CONTROL SYSTEMS, INCLUDING PHASE ANGLE VOLTMETERS USEFUL TO MEASURE BOTH MAGNITUDE AND PHASE ANGLE OF SIGNAL COMPONENTS, RATIO BOXES USEFUL FOR DIRECT READINGS OF NULLS, PHASE ANGLE SHIFTS AND QUADRATURE VOLTAGES, INSTRUMENT SERVOS USEFUL FOR MEASUREMENT, REMOTE DISPLAY OF DATA, DATA CONVERSION, CONTROL AND COMPUTATION, A.C.D.C. CONVERTERS USEFUL FOR MEASURING TOTAL SIGNAL, QUADRATURE, IN-PHASE AND FUNDAMENTAL COMPONENTS, AND THE LIKE