European hinges must be mounted so their arms are 90 degrees perpendicular to the edge of their door. If they are not, then the hinges will bind and wear excessively over time. I struggled for a long time trying to use a combination square to make the alignment. Then I devised this simple jig. Here’s how it works: Set the hinge in it’s hole, hold the hinge arm against the jig, and at the same time hold the jig against the edge of the door, then drill screw pilot holes using a self-centering Vix bit. It doesn’t get easier than this!