A chaotic pendulum

At the last day of a short stay in the UK I walked the city center of Bristol.
Interested in architecture I entered the St. Mary Redcliffe church.
To my surprise inside a so called "chaotic pendulum" was in operation.

I watched the pendulum swinging for quite some time but could not see any regularity.
The movement was totally chaotic.
Below is the text next to the pendulum:

A lesson in modesty.

and finally the brochure of this beautiful church: