I maintain my shaptons with a piece of Iyo stone abot 1/3 the size of my Shaptons. Once in a while I check to see if they are flat with the DMT, but doing it this way cleans and leaves a scratch free surface that feels the best for me. I start on the ends where the wear is less and lightly bring the slurry over the rest of the stone. They stay flat for a very long time this way.