Thanks for clearing that up... thats why I talked about "equivalence" and grit seperately. Sorry for the confusion.
its actual grit is measurable (the size of the garnets) but unfeasible- and I promise will be almost nothing like its "grit equivalency".
What I meant is the true grit of the stone, as in its cutting particle size, doesn't necessarily mean much when comparing two stones, or even the same stone under different conditions.