Quincunx Board

One of the golden rules of quality engineering is understanding the difference between common cause and special cause variation. I love to talk about it. Doing so adds a bit of pitch to my voice. But I'll admit it took me some time to truly understand the concept. I had heard it from others and agreed with the principle but it wasn't until I saw a quincunx board experiment that the light bulb went off in my head.

The board has been around for a long time. It was invented by a mathematician named Gallo in the 1800's. Pictured above, it works by dropping a series of balls through rows of precisely located pins. Each ball, as it hits a pin, has a 50/50 chance of falling to the left or right. When the balls pass through all rows of pins, they fall into a slot or cell. The shape of the ball's distribution forms what looks like a bell shaped curve. This 50/50 behavior represents common cause variation. The pins can be adjusted to show the effects of special cause variation.

The value of this "factory in a box" (as it is often called) is being able to quickly simulate processes or tests that would be impractical to perform in real life. Included in the simulations are statistical inference, process centering, random inspection, control charts, pre-control, and process management. In the simulations, concepts become visual as the output matches the math.

Quality Minds, Inc. uses a quincunx board in its services. We would love to demonstrate the power of this device to you.

Here is a link to an applet that depicts the quincunx board in action:
http://www.jcu.edu/math/isep/Quincunx/Quincunx.html