There is no set dimension to use when adjusting headlights. It all depends on the ride height of your specific car. The same procedures are used whether you are working on a lowered sports car or a lifted 4x4 truck. Even if your headlights are severely out of adjustment, the center beams will still be in the correct place When you pull your car up close to the wall. The adjustment comes when you move the car back to the 25 ft. mark. Once it is at the 25 ft. mark you will be able to see where the beam is projected out in front of the vehicle. That will allow you to make the proper adjustments to get the "light beams' pointed in the correct location.