Well, I decided to get a square I could trust so I forked out some $$ for the Starrett 12" 4 piece set. It was on Amazon for $230. I checked all the head and they are "dead on balls accurate" as Mona Lisa Vito would say. I had bought a PEC hoping to save a few bucks, but the protractor head was off by about 1-1/2 degrees so I sent it back. The protractor head in the Starrett set is much nicer. If you just want the square and center finder, the PEC would be fine, but I wanted a really good protractor head so this will serve well.