Grammar Resource - David Mentions a Certain Book

Howdy Y'all,

A couple of times, in the grammar series of classes, David mentions a few resources he uses for the grammar rules he is teaching. One is CMOS (Chicago Manual of Style). The other title had something to do with grammar usage I believe, but I cannot remember the name of the book.

Rather than re-watch the entire series of videos, I was hoping someone here would remember the title, and maybe even the author, off the top of their head.

Thanx for the assist