Undo now works nicely for Dials when using the mouse wheel. On one hand, this feature is frustrating, because it was a lot of tricky work, and the results are completely unnoticeable. But on the other hand, the fact that it's unnoticeable is exactly the sign that it works well -- you don't even notice that it's working well, because it just quietly does what you expect. Back when I worked on scaling server infrastructure, we often said that "if nobody notices that we did anything, we're doing a great job." I think that applies here as well.
Of course, while fixing this bug, I found others. For example I noticed that the undo/redo hotkeys sometimes don't do anything, and I think it has something to do with which GUI component is focused, because clicking on something usually fixes the problem. I also realized that I'm still not satisfied with the Dials, so I'm going to do some sketching for what a better version would be.
