Thanks folks. I did use a straight edge, of a sort, to make the dadoes in the shelf of the prototype. But it required several steps of setup to cut both the horizontal and vertical dadoes in the underside of the shelf. What I want to do is position the shelf once, then cut both the vertical and horizontal dadoes with the shelf in that one position.
Rethinking the dadoes for the shelf supports, a jig may not be necessary because there's only one edge that requires a stop and a straight edge set correctly would work.
Occasionally looking back will help you avoid hitting those thing you will hit if you constantly look back.