D'you mean to set the toe-in?

Make a trammel bar of scrap wood with a nail near the end and another nail positioned so that both nails are at roughly the center of each tire. Wrap masking tape around each tire and level the tapes with the axle ahead. Poke the nails through their respective tapes. Level the tapes with the axle to the rear. Put one nail in a hole already made, poke the other nail into the other tape. The distance between the holes in "the other tape" is the toe-in, positive and wrong it the new hole is outside the old, and negative and right if the new hole is a few millimeters inside the existing hole.

I hope that you will tell us how you satisfy your obsession to be compulsive disorder in setting the handle bars parallel to the average line of the wheels.