Nobody but VA seemed to give a shit on Discord or in the grid patterns thread, despite how important this seems to me, so I'll bring this here.
Look at this post from RSA #8 in January:
It's from someone's private messages with VQC back when he had a Twitter account. VQC quite literally already told us what "root of d" is. It's a cell in (0,n).
"Root of d = {0, 2xd, 3xd, 2xd, d, 9xd}. All a and b of ( 0, 2xd, t) are multiple of d for all t."
Also root doesn't necessarily refer to square root. It can also refer to the root of a tree.