Unfortunately there simply aren't very many math professors. An average American school district has 200 teachers, all of whom would have used chalk until recen

Unfortunately there simply aren't very many math professors. An average American school district has 200 teachers, all of whom would have used chalk until recently, that's a lot more than there are professors in a university math department and there are many more school districts than universities. I agree that there is a durable market for chalk, but not at this kind of volume.