Jerry - you can do exactly that with my Fritz and Franz jig.? You can set the stop on the front scale to the desired location and then slide up the back portion and set its stop exactly the same as the front to get a parallel cut.? In practice, I find my stops to be quite accurate so I can use the scale on both stops and set them to the same value independently and I'll get a parallel cut. I believe this is what Tim showed in his photos in a previous post and he is within 0.001"
David