roger lance
The DMT Dia-Flat stones (which are more expensive than the die-sharp stones) come with the following statement...."all of the DMT Dia-Flat stones are carefully machined to be flat within .0005 inches".....and that I believe was over the entire stone surface. That's pretty flat.

Its also my understanding that DMT will exchange stones if you get one that is out of spec. That's why it might make sense to go to a local store and buy in person after making an inspection so you know what you are getting.

I'm not an advocate for DMT or Woodcraft; but, I must say that I've been impressed with some of Woodcraft's sale promotions of late.....prime examples being some specific Japanese pull saws at 50% off. Like anything else, buyer be ware.....pick and choose with care.