Braided Galton Boards – Visualizing Probabilities with String

I’ve been playing around with Galton Boards recently. They’re an awesome demonstration of the central limit theorem, and how several independent 50/50 events sum together to make a Gaussian/Bell curve.

Seeing the standard Galton board gives an intuitive feel for how random variables behave, but it takes time to run the experiment and see the results accumulate.

I wanted a more immediate visual demonstration, and after a few prototypes I settled on using a thread to represent each possible path through the system:


I used 12.5mm dowels cut to size, and hammered into the lasercut wood.


The 64 and 32 string versions

The strings are cut to length, then held in place with a screw clamp and threaded through one at a time:


Stats and craft therapy all in one

It might be because I finished this late at night, but I found it very difficult to thread without making a mistake. The strategy I ended up using was to hold the previous thread in my left hand and the next thread in my right. By jiggling my left hand I saw the old thread bounce, which gave a good reminder of where I was in the sequence, and hence to put the new thread in the right spot.


Files here for anyone that wants to make their own:

It took a bit of prototyping before I got a form factor I was happy with. Here’s two of the failed attempts, that I avoided because they either weren’t practical, or they were slightly too opaque a display of the concept:


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2 Responses to Braided Galton Boards – Visualizing Probabilities with String

  1. Pingback: Turn Binomials into Gaussians with Polymer Clay | Tinkerings

  2. Pingback: Improved Braided Galton Board | Tinkerings

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