This exhibit features a low table etched with evenly spaced lines. When you toss some chips on the table some of them will cross a line and some will not:
Using a calculator at the exhibit you can divide the number chips by the number of crossings. The more chips you throw the closer this ratio gets to pi.
This surprising method of calculating pi, known as Buffon's Needle, was discovered by accident over 300 years ago by a French mathematician–Count Buffon. He wanted to calculate the odds of winning in a then-popular game of chance, where you tossed a needle onto the floor and bet on whether it would land on a seam between the floorboards.
Statistically, the more tosses you make, the better your estimate of pi will be. Notice how the average result in this graph improves over the course of sixty trials (click to enlarge).