The "normal distribution" is a useful reference for all kinds of probability problems. If you ever make graphs of certain kinds of statistics — the heights of adults, the weights of babies, classroom scores, etc — the results tend to form a bell curve. It's a neat concept, but its significance can be hard to grasp until you see it happening for yourself, over and over again.

The Galton Board by Four Pines Publishing is a desk toy that lets you do just that. After the 3,000 steel balls have accumulated in the hopper at the bottom, flip the board over and watch as they cascade through 12 levels of branching paths into the row of bins below. Time and time again, the stacks they form end up approximating a bell curve distribution. It's pretty sick.

Watch this delightful video to see what I mean:

Redditor "MorningPants" succinctly explains what's happening here:

When a ball hits a peg, there’s a 50% chance for it to go left or right. So for it to fall in the leftmost slot, it would have to go left every time. For it to fall in the middle, it has to go left and right the same number of times. There are lots of ways that can happen, so more balls end up in the center than on the edges. This creates a predictable distribution pattern marked by the dark line.

Like the magnetic field demonstrator set I recently wrote about, the Galton Board would be a great toy to keep on your desk or in a classroom environment.

Get it for $50 on Amazon.