I guess I'm cheap, for $200 I can sweep a lot of table. Instead of bumping into the T slots, I use two .050 Jo blocks, one at either end of the sweep. I position the indicator abut eight inches from the spindle, this gives me 16 inches of sweep, not four, it's at least four times more accurate (no, not accurate), meaningful. When I get it within .0005 in 16 inches, that surely seems closer to square than .0001 within 4