Thanks for the link, Jorge!

My graph was hand-drawn, and my emphasis was a bit different: Everything is based on 10s exposure with very light gray (zone VIIŻ?) placed at a reading of 85 or thereabouts. I then read midtone and shadow: Midtone to select the paper type, shadow to select the grade. Then dial in filtration, adjust aperture and ND filtration to put the very light gray back where it belongs.
I also have readings of a projected Stouffer grayscale, and prints at 10s on more than 20 paper/grade combinations...