26 TEMPERATURE, PRESSURE, HUMIDITY, TIME, LIQUID LEVEL, AND FLAME RESPONSIVE CONTROL VALVES, SWITCHES, AND POTENTIOMETERS; THERMOCOUPLE OPERATED CONTROLS, RECORDERS AND INDICATORS; FLIGHT TEST RECORDERS; SIGNAL CONVERTERS COMPRISING AN AIR SPEED, ALTITUDE, ATTITUDE AND/OR POSITION RESPONSIVE SENSERS FOR OPERATING SWITCHES,VALVES OR POTENTIOMETERS OR THE LIKE; SCANNING SYSTEMS COMPRISING A SIGNAL GENERATOR AND A RECEIVER FOR REFLECTED SIGNALS FROM THE GENERATOR FOR LOCATING OBJECTS; GYROSCOPES; AND ELECTRIC CIRCUIT ANALYZERS SUCH AS VOLTMETERS AND ELECTRIC LIGHTS HAVING PROBES FOR BRIDGING CONTACTS OR ELECTRIC UNITS FOR TESTING THEIR OPERATION