Do the numbers matter? I think so. But I try not to think too much about why so.
I prepared 8 more papers (8" x 8") squares with 3 layers of a middle grey guesso.
I sanded them with a super fine sandpaper that had a bit of graphite muck in it. I like to keep these bits of dirty tools around to see what will happen. Good dirt. This is a ritual of preparing surfaces while getting acquainted with proportions of these 8 inch squares.