The Shun Leveling Stone helps maintain any Shun Whetstone. Over time, a whetstone will naturally wear in the middle, creating a concave surface. Yet to sharpen your knives efficiently, a whetstone must be perfectly flat and level. That's where the Shun Leveling Stone comes in. Just soak both the leveling stone and whetstone in water, then move the ridged side of the leveling stone over the surface of the whetstone until the flat surface is restored. The Shun Leveling Stone is easy to use and will give your whetstone even longer life.