One problem I have with this program is that when drawing any type circle, it is confusing at first. To make the circle larger, you must press the up button. To me, it is natural to press either right or left. This could be fixed with a simple "or" instruction placed when sizing the circle [which I have done on my calc..]. I wouldn't say this is so much a bug, but had I not went into the source to see what was up, I would have surely reported this as a bug. I recommend, though it isn't necessary, to make circles be able to be created by pushing right and left or up and down. It is just more natural to me.

Also, the fill function, though it's a great idea, is a tad flawed.. it seems to never fill in all the way and takes a drastically long time to do it. Suggestion: Take it out.