Since you are not using the ruler to rotary cut with, it would be easy enough to make your own ruler by cutting a piece of template plastic that is 5/8" wide with a line down the center.
I've always drawn a grid of squares 1 inch larger than my desired finished square size on the back side of my lighter fabric then draw lines through the center diagonal, next put this and a darker fabric right sides together & sew 1/4" from the diagonal line cut on all of the lines. A person could use the 5/8 ruler (home made) instead of trying to guage the 1/4+ at the sewing machine.