Tips for measuring ramp test distance

I set the ramp, run the laser across it. Move the laser head to the best focus position then use Drill bits between the head and the ramp to give me the distance.

Eg, if I can fit a 9mm Drill between then obviously 9mm focal from end of lens tube. If your distance is bigger then fold a piece of paper to fit between the lens tube and the ramp then measure that.