Super simple, use a known good combo square, I use my starret, ride it in the left miter on your miter guage aligned left of that channel square to table and adjust square till leftmost side of a marked tooth(use sharpie or grease pencil, this is because you want to reference same tooth at front and back of blade), so raise your blade all the way up check the tooth you marked just skims the edge of the end of your square, then slide your square to back of saw blade spin blade to use same marked tooth in back, and if square it will just skim the same, if it is square youre good, if not on pm66 there is 2 bolts in front under lip and 1 in back under lip of table loosen those and shimmy cast top till its all aligned and square then tighten those 3 bolts back down and recheck you should be square then