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I'm trying to remember if this is what the old-timers called a "tump mortar." It was made with a wooden mortar with higher sides and used to "grind" grain.
I just don't see what that accomplishes, that couldn't be done more easily manually. Or is that like a miniature version? It doesn't have enough force to accomplish much, and the small amount of whatever is being pulverized baffles me. A mortar & pestle seems to be a lot more useful, though it isn't water powered.