I LOVE this thread! I get all wound up in trying to understand stuff like this and have to draw diagrams too. The REALLY funny part is that I am a statistician and I have been TEACHING statistical analysis at various universities for 40 years! But it's a different kind of math. You would not believe the scrapes I've gotten myself into with "quilting math" -- especially when someone else asks me questions because they assume that I must be an expert!