Align one board on the left side of the jig, and cut the joint.
Flip the board top-to-bottom and keep the SAME EDGE aligned with the left side of the jig, and cut another set of fingers.
For the next board, align it on the right side of the jig. Cut the fingers, the flip the board, again keeping the SAME EDGE aligned with the right side of the jig.
Sometimes you will get a small amount of tear-out from the router bit. This is normal and happens no matter what kind of jig that you use. Some people deal with it by clamping a backer board to the workpiece. Another method is to use boards that are slightly thicker and plane (or sand) them to final thickness after you've cut the fingers. Another method, adopted by people who are making drawers, is not to worry about a small amount of tear-out because it's hardly noticeable.
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