Did you know that when Pope Julius II asked Michelangelo for his credentials before painting the Sistine Chapel Michelangelo replied by painting a perfect circle freehand*. The man knew he was badass. But who do you know that can draw a perfect circle? Not I, senhor. So, I will show you some 'not one of the most talented people to walk the earth' ways to make a perfect (or close enough) circle, without many tools.
*right, I was told this story by my favorite Art History teacher in college. May not be true, but she did know how to keep us interested.