Why are they called Berger dots?

According to Joe McKeefery of E. I. duPont de Nemours & Company, in the days before PC and electronic processing of Words, one of the most prevalent options for listing items in a report on the typewriter was the small or large O. Mr. Berger, another duPont employee, started coloring the insides of the O so that they stood out better, and soon everyone (at duPont) was doing it. Hence, the name "Berger" dot.