The 7530T and 75301 both have a TimeRev function mandated by NHRA. In essence the way that the TimeRev function works is after x amount of seconds (from 1 to 12.5 seconds) engine RPM limits to a preset RPM limit (from 1000 to 12500 rpm). By default it is set at 9.0 sec @ 2000 rpm. What this means is after 9 seconds the unit will limit engine RPM at 2000. If you dont know its here and have to drive the car back up the return road or the car isn't running a 9 second pass the engine rpm drops to 2000 and will not reset unless the dark blue wire is cycled to 12v.