Students of Lean Six Sigma will be interested to see a practical demonstration of the central limit theorem and  normal distribution. The demonstration was invented by Francis Galton ( University of London ) in 1894 . The demonstration consists of a vertical board with rows of pins. Balls are dropped from the top, and bounce left and right as they hit the pins. Eventually, they are collected into one-ball-wide bins at the bottom. The heights of ball columns in the bins after hundreds of balls are dropped will approximate a normal distribution curve ( bell curve).   This is an excellent practical demonstration of how random variation in the inputs to business and manufacturing processes will cause values of the outputs of the processes to vary around the mean average values in a distribution that follows close to normal distribution.   Very good Youtube video showing the Galton Machine and the dropping balls here