Zwilling Twin Stone Pro slipsten 250/1000 is a sharpening stone with two sides, one coarse and one finer. The lower the number (250), the coarser it is. Start by wetting the sharpening stone and then draw the knife edge against it. Begin with the coarse side, which is meant to remove nicks and scratches in the edge. Finish with the finer side (1000) to polish and achieve that razor-sharp edge.