Just for shits and giggles I grabbed a random book from the shelf and counted characters per column. The book I grabbed was "Spoken Language Processing", Huang

Just for shits and giggles I grabbed a random book from the shelf and counted characters per column. The book I grabbed was "Spoken Language Processing", Huang Acero, Hon (ISBN 0-13-022616-5) and I counted 88 characters per line. The book is still very readable, despite exceeding the claimed 70-odd character limit for books/columns. Another book sitting next to it (a numerical mathematics textbook) had 82 characters per line. Granted, the limit of no more than 70 characters per line applies if whitespace and punctuation aren't counted, but that's never done with hard limits in digital documents either, so...