This is lovely.

> Sometimes (not always), this makes addition visual

I wonder how often - my suspicion would be rarely.

Seems like it's only when adding 1 + 4, 6, or 8 in a place value or where one of them is 0. It doesn't seem like it'd ever hold across a carry, but I could be missing something.

Edit: There's actually a few cases with adding 2 as well!