Ye thought about scanning the gauge, might be the easiest option.

So Jazz what your saying is put the spindle in the middle of the bed, insert a piece of steel, say a 6mm rod as that will probably be the max shank size. Have this steel rod go down to the bed and bend 90deg and run parallel to the bed, touching it. If its square then the rod should stay flush to the bed along its length, and while I spin it around the bed 360deg..?