So it looks like that paper is about grade 2.5-3, if I read it right.

I see how the 21-step wedge is used to measure the range of the underlying exposure, but is
all I need? Because I don't quite understand where the thirty-one-step exposed wedge underneath the 21-step wedge comes from. It seems like I need a 31-step wedge to contact-print onto my paper to start with, to duplicate what is depicted in that figure.