9 SIGNAL MEASUREMENT, ELECTRICAL, TESTING AND SCIENTIFIC, INSTRUMENTS AND EQUIPMENT, AND APPARATUS FOR MEASUREMENT OF SIGNALS AND FOR CONTROLLING BRAKES ESPECIALLY INTENDED FOR UTILIZATION IN THE AEROSPACE INDUSTRY-NAMELY, BATTERIES, STORAGE CAPACITORS AND CONDENSERS, ELECTRI-VALVES AND SERVO-VALVES, OSCILLATION REDUCING UNITS FOR SUSPENSIONS AND STABILIZERS, CIRCUITRY FOR BRAKES AND BRAKE CONTROLS