The quincunx, also known as the bean machine or Galton box, is a device invented by Sir Francis Galton to demonstrate the central limit theorem.
The central limit therom demonstrates the law of error and the normal distribution.
The machine consists of a vertical board with interleaved rows of pins. Balls are dropped from the top, and bounce either left or right as they hit the pins. Eventually, they are collected into one-ball-wide bins at the bottom. The height of ball columns accumulated in the bins will eventually approximate a bell curve.
Among its applications, it afforded insight into regression to the mean or "regression to mediocrity".