The cover image is the probability distribution of throwing six-sided dice. The image at the far back is the flat distribution of throwing a one through six with one die. The one in the foreground is what you get when you throw five dice - it approaches a normal distribution. You can get some very new insights when you have the third dimension to play with!
https://www.amazon.com/3D-Printed-Science-Projects-Engineering/dp/1484226941/
