History

Today I saw a tree trunk with something attached to it. A closer look revealed that this was like a history lesson.
Someone, most probably Prof. Dr. Friedel Sauerwein, had put several marker arrows, pointing to tree rings and different historical events. From the French revolution in 1789 to the fall inner-German border in 1990.
A tree nursery is called "Baumschule" in German. Literally Tree-School.
An interesting way to teach history AND the meaning (and importance) of tree rings.