This is a bookmark I don't want to lose track of, but which I can't pin since it's a pdf. It's polar graph paper. I know, fascinating, right? ;)
So, if you happen to have a need for this, you're welcome. :) If not, ignore it as just for me. Or rather, for my son and resident mathematician.
here. And, if you'd like, you can also visit my Math board on Pinterest, where I keep track of stuff like this.