I checked my naniwas today and notice they are not completely flat. I checked them with a metal straight edge. The 1K has a little rise in the middle most of the way long ways. the others you could see light between the straight edge and stone on a few places. the flattening plate with the same straight edge showed no light. I use the diamond plate after every honing session. and I us it under running water. I know that there is no way for a hone to be completely flat but how off can it be and still be effective. Just a question for the more experienced hone masters.