I had a cardboard 26" circle I would measure roll out with at different tracks, even on Sat & Sun on two day events where you could get bit if the roll out changed. This was using a delay box I typically aimed for a .015 light but learned how to judge the darkness & changing starting line conditions. I used a amber lens during the day & clear at night to offset the conditions. Keeping a detailed log book helps alot. It's much tougher with street tires & foot braking as your launch stall can vary.
