I think the "black square block" is nothing more than some type of carborundum stone. Cecile's method is tried and true. He did a great job of it!!!
I've used the method he shared and it's a great one if all you have is the big stone itself spinning and want a less expensive "hand method"of truing the spinning stone. This is the "tradtional method" for truing sharpening stones of this type. I'm not familiar with any other methods other that a "bushing wheel" but that is a tedious method in my experience and view of it.
I find the diamond stone works so fast that truing even a badly out of true stone goes really fast. I've never had one take more than about 35 minutes for the worst of them...most in lest the 10 minutes of work.
