If he is refering to multiple spark boxes then my crane is the same thing and it works fine. ZEATER also has MSD with the same light and it works fine. I have not compared it to a standard light but then I would have to rely on accurate advance marks etc etc. Who really knows. If I click the light down 5 degrees it moves 5 degrees on the timing chain cover marks. Besides, find me a light or someone that can set the timing and by the time you tighten the dist etc you are probably off a degree anyway. As long as you stay with one light and tune from there you will alway's be consistant. If you had a $50,000 race motor then I would worry about a degree here or there but otherwise just use it for a tool to go up one degree or down one degree. It is perfect for that.