Bean machine

The bean machine, also known as the quincunx, is a device invented by Sir Francis Galton to demonstrate 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 randomly left and right as they hit the pins. Eventually, they are collected into one-ball-wide bins at the bottom. The height of ball columns in the bins approximates a bell curve.

See also

• pachinko

External links

• Simulation of the bean machine at RAND
• A longer article on Sir Francis Galton and the bean machine
• Another simulation, with explanations http://www.ms.uky.edu/~mai/java/stat/GaltonMachine.html
• Yet another simulation, from John Carroll University http://www.jcu.edu/math/isep/Quincunx/Quincunx.html