Why not just use a straight edge to check it for flat? Not sure about everyone else but mine was flat. I used the slurry stone a couple of times, but my really well worn DMT. Is what I use now to raise a slurry if I even do that. When raising a slurry on the Zulu its doesn't raise a milky slurry so no need to work it hard, it'll break off some grit for you. I've said it before, it's a stone that's really hard to overdone on. My routine with my naniwa is just a couple laps to refresh, on the Zulu a hundred or so. It doesn't get used much. But a great finisher in my opinion. Tc