I did these for the first time more than a week ago. I wanna do more and move up to three values but I fucked up my wrist lately drawing too much other stuff. The first ones at the top I had no idea what I was doing but I think (?) I started getting it by the time I hit the bottom images. I was actually asking if I did these correctly but I didn't get much of an answer before.
I started doing these at the recommendation of this artist and people who mentored under him. The idea is moving up from 2 to 3 to 4 values either with the same study or new ones until you get pretty proficient at it.
https://youtu.be/6FOJc04-UKU