Diamond Stones - What's the Difference?

In japanese tools, there's an element that almost like flatness is sort of a sort of a god. If you don't have the back flat, what happens is the plane don't meet well for at all and you can't get that sharp. What's valuable then is a stone that stays very flat. And so these diamond stones are really modern thing that people are using. But they're also intensely tricky tubes flattened, because they will annihilate anything that tries to flatten themsike.