Interesting...my book says 25 feet. I believe what they are alluding to is, after you've set up the car as per their specifications, (2 people or weights, parallel to the ground, etc.) you measure the distance between your headlights and the height above the ground and mark it on the board. Then, with the board at the 25 foot distance, you adjust the beams with the screws until the pattern on the diagram is achieved. At least that's what I got out of it. Kirk