I managed to get quite a few features in here with help from Duane and Anurag. My favorite is the “inspect zero” feature towards the end of the behavior. I’m also pretty happy about the automatic range on the y-axis on the final graph.
It does run a bit slowly because I have a lot of answer checking and references. I’d love for people to go through a few versions and tell me if there is anything sticky or give me suggestions on where to add feedback or hints to students.