any light wether digital or resistor dial will get screwed up on msd style ignitions in the rpms its throwing out extra hits . stick to a std. one and use the degrees on the balancer .
snap ons big digital had a class action suite against it from race teams that wasted motors due to it picking up the middle or last spark and then the time was way advanced up stairs .
the old fox valley , craftsman chrome ,msd and flaming river batery were tested most accurate time and time again