The article doesn't clear up the mystery, but this explanation sounds the most convincing to me: > "You had to use something when you were typing because you w

The article doesn't clear up the mystery, but this explanation sounds the most convincing to me: > "You had to use something when you were typing because you would write two or three paragraphs on deadline," Harrison says. "Then the copyboy would pick it up and send it to the composing room. It was necessary [to have] some way to say, 'This is it, it's over... Put a head on it and put it in the next day's paper.'" So it used to be part of an ad-hoc protocol for sending paper messages from your typewriter to the print shop, and the "-30-" was what EOF is today?