if I need to square up from the middle. I find the sz I need. I take a pc of template plastic, cut it to that sz. Take a ruler & a fine sharpie marker, draw a line from corner to corner(diagonals). center it over your block middle, carefully place your ruler on top, & rotary trim away the small edges.save the template to reuse or recut!I know you can square up from your rulers, but I find it MUCH HARDER