This is actually my first post on SRP - so happy I'm finally getting involved. I'm much more active and knowledgeable in the knife community at kitchenknifeforums.com, and have a respectable collection of Jnats, with a dozen or so other hones from around the world, as well as a dozen or so synthetics. Anyways, oddly enough, I've found it nearly impossible to find an answer to how grit is determined in synthetics (this question can't really be applied to naturals as we use synthetics to reference estimated grit in naturals, and the abrasive density is much less uniform in naturals than synthetics, obviously).
Does anyone know, especially in JIS and AISI? I think I once read long ago that it's the average density of abrasive particles in 2.5cm^2, but that seems like an odd and arbitrary number. Any insight would be appreciated.

Thanks!