Heard this tip from someone else on web and it works. Try using a 2' x 2' of 3/4" square of MDF sheet goods. Most big box stores sell them for cheap as a project board. Pick one that does not have destroyed edges. It gets me to within cabinet square tolerances for setting up my MFT/3 with a touch of sanding of a few high spots. I usually find the squarest corner with my machinist square, then cut a diagonal to give me a lighter triangle at the end of one of the legs from that square corner. A quick cut off of the corners of the triangle and you should be good to go. Once the table is set up, I put it away so the edges are protected, till I start my next project, and I check again for square before starting. This usually passes the 5 corner test for square with a woodworkers needed level of accuracy.
The Dash-Board from Rob is awesome. I have what you're referring to as the older version (black and silver) and I'm no longer frustrated when I have to change the guide rail bracket height. BTW, the setup square from Woodpeckers, if it's the one I'm thinking of, is phenolic.
