To expand on this method of ripping using spacers, you might like using two of Incra's original jigs (about $50 each) as adjustable spacers. Once calibrated alike, simply place between dogs and back side of rail. These original Incra jigs can accept either Imperial or metric scales, and thus can be set to increments of 1/32" (Imperial) or 1mm (metric).

Have fun!
Corwin