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Thanks Charles. I can only think it must have been caused by the one wet spent grinding tool on top. The grit seemed to last about twice as long as mirror on top so could it have been doing enough to counteract the normal action of the W stroke? I quote the stellafane ATM guide to strokes: "Use Mirror on Top to deepen the sagitta and shorten the RoC and Focal Length." At a 0.5mm sagitta the RoC is 7225mm which is longer than what I'm aiming for. I've read that sometimes it can be a good idea to go a few tenths of a mm past the required sagitta and work tool on top for the rest of the grinding. Is this a good idea? Should I go back to 80 for a few hours longer and get to 0.8 mm, I've got plenty of 80 grit left over?
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