OK Richard, you've got me wondering. I've seen millstones, around here they were pretty darn big. More than a few of them got dumped over riverbanks here and there to keep the banks from washing away. I like to canoe, I've wanted to load one up and bring it home many a time. If I could lift one, and if it'd fit in the canoe. They're just too big. So how did the miller keep the stone shimmed up so it didn't touch the one below it. I know the bottom stone was stationary, but that big ol' stone on top spinning around, it seems like it would just grind through anything. Any sort of shim, steel, anything, would quickly get ground away. Did they raise the axle that the top stone spun on? Even then, those stones are so heavy that it seems like it would be a continual job maintaining tolerances. I also seem to remember reading something once about "dressing" a millstone. Do you know if that had to do with cutting the furrows that fed the ground meal out to the edge? I'm attaching a link to a rebuilt local mill that I just love. I think you might enjoy it. The mill has been there for two centuries. It's recently been rebuilt and is back in operation. A labor of love by some really good people. You'd have fit right in.