26 ELECTRONIC SENSOR-RESPONSIVE ENGINE ALARM UNITS FOR PROTECTING ENGINES FROM FAILURE OF CRITICAL FUNCTIONS; DISTILLATE CONDUCTIVITY METERS; OCTANE ANALYZERS; NITRIC OXIDE OPTICAL DETECTORS FOR MEASURING OXIDES OF NITROGEN IN EXHAUST SAMPLES FROM MOBILE AND STATIONARY SOURCES; PUSH BUTTON OCTANE NUMBER UNITS FOR DETERMINING OCTANE NUMBER OF MOTOR FUELS AND DELTA STREAM OCTANE NUMBER DATA UNITS FOR CALCULATION OF DELTA ROAD INDEX