Not flat, has numerous saw marks on surface.

The quality of this Spyderco ceramic stone in Ultra Fine is not commensurate with the Spyderco name. The stone is not flat. It has numerous saw marks. It took me more than 2 hours to flatten and polish out the saw marks using a progression of diamond plates. The process of flattening stone also put a lot of wear on my diamond plates. At first, I used a 1200 grit diamond plate to give it a nice finish, but it turned out to be too fine. The resulting surface was too smooth to hone steel effectively. Now it finished the surface with a 600 grit diamond plate, which gives the Spyderco ceramic ultra fine stone an equivalent 6000 to 8000 grit finish. Even then, it's still too fine. I may rough it up with a 400 grit diamond plate or even lower. Overall, I'm not happy with this Spyderco ceramic stone.