The ET timing starts at the same time the reaction timing stops. For example , if the light turns green and I wait 1 sec., then launch and run a 11.0 sec. ET , the time from the light turning green till I cross the finish line will be 12.0 sec .However , if a better drag racer drove the same car and had a .005 reaction time then his time from the light turning green till crossing the finish line would be 11.005 sec In both cases the ET stays 11.0 but the better racer wins because of a faster reaction time.