Once I was sitting outside an ice cream shop and the conversation at our table died. Somehow that evolved into a group determination to empirically evaluate pi with the materials at hand. Well the materials at hand were exceptionally well suited to the task. I had a tape measure in my pocket, we had leftover chalk from making a sundial (well a sun clock of sorts) on the wall, and a bicycle.
I chalked the tire, ran it along the sidewalk, and measured the distance between the two resulting marks. Then I measured the diameter of the tire. Only then did I pull a calculator out of my pocket and take the ratio. To my amazement, the result was 3.142, rounded. I was expecting something between 3 and 3.3 but geez Louise. What is the probability this occurred by chance?