There is an article by the Public Domain Review[1] where they present an old book about sketching on a blackboard. I've been wondering how often would a regula

There is an article by the Public Domain Review[1] where they present an old book about sketching on a blackboard. I've been wondering how often would a regular teacher make such elaborate drawings. Considering this completely arbitrary and small sample, I guess the answer is "often". [1] http://publicdomainreview.org/collections/blackboard-sketching-1909/ http://publicdomainreview.org/collections/blackboard-sketchi...