Richard H.,
Something to consider . . .
the thicker pro stones (and any other thick stone that has not been glued to something e.g., wood or glass) one can sharpen on both sides of the stone. Now why in the heck would one want to do that ?
I keep one side very flat for finish blade work and blade back work. The other side of the same stone I don't fret over as much and use for cambered edges : jack, scrub and chisels etc.
How do I keep them straight ? I write the grit number on the edge of the stone with magic marker (while the stone is dry) ; the number right side up has the flat face up and . . . well you get the idea . . .