I recently bought a Black Hard Arkansas stone and was curious what is the grit size. How do you figure this out? Experience? Comparing to known grit stones? It seems to put a polished edge on my razor but I'm not sure if I need something higher in grit to finish the razor. Under 60X microscope it looks better than my HSB & Co.'s OVB dry barber hone.

On a side note, does barber stones need to be flattened ... if so, what is the best way of doing that? Also, since I have not flattened the hone, would that be why the Arkansas stone makes the razor look better?