The device would be impossible. When you use sandpaper you automatically begin to wear down and take off paricles, therefore a particle measurer and particle counter wouldn't work. Also, only grits that are like 600 or higher have a uniform grit, where there is the same amount of particles in the same concentration for every square milimeter. The lower grit is more like: "ya throw some glue and sand on there, whatever"
And brian, I have like 5 sheets of 800, i love the stuff, not too rough, not too fine, good for taking off small bits of wood atta time.
You guys are losers! I mean come on! You can usually tell the grits apart by colors. The lowere grits like 80 are allways brown, and etc. Also, just train your fingers. Maybe it's because i have sensitive fingers, but i can tell 1200 from 2000 or 80 from 100 any day just by feel.