I just received the Starrett 6" and immediately ordered the 12. First I tried to rejuvenate an old one that belonged to my father. After a half hour of scrubbing, de-rusting, and fine polishing, I thought I had a twelve. I checked the depth accuracy, and it was right on. Then I checked it as a square. Although the end to end was correct, the center of the ruler had been accidentally ground. So if I tried to square up a 4" high table saw blade for example, it would be off. That was all I needed. I went to the computer and ordered the 12 as well. You can't afford to screw around with the device that all other tools are measured by. A cut only off 1 degree creates a 91-degree edge. When gluing and clamping that edge, it bows or skews your project. Then when you try to mate that up to a square project, it doesn't fit. Save yourself a lot of heartache, time, and money, get a starrett combination square.