If you take a car of a given weight, and run it down a given distance, regardless of time elapsed..the speed will always be the same. Run in 3rd gear. GO thro all 3. the horsepower applied over that distance will result in the same mph. (IE the Moroso drag calculator thingy) It's not exact, but it is much more precise than any chassis dyno. Chassis dynos should not have numbers associated with them. The numbers mislead. All one needs to know is it making more power than before. Not "6hp" or "20hp" more. It's a tool. A fun, big, loud tool. Nothing more.