Basically it is just a random line that usually just marks the scale to the wedge. Sometimes I have the wedge glued on one side, so I only have to mark one side. It is to give me a point to line up to. Typically what I am effectively doing is pulling the scale out of alignment by 1/64 to 1/32, so when it gets taped and drilled I want to be able to get it exactly where it was for my test fit. I also want to point out that because of this the end always has a small amount of reshaping to do. By doing this the wedge end will not be perfect anymore.