What is the fine-grained topic of the following text: In the last third of the 20th century the Cameron Belt press utilized letterpress technology using a flexible polymer-based plate to print an entire book at one pass, an achievement made possible by a simple mill-wheel like device which collected in order one each of the 4-page sections delivered by the press before turning on to collect another book and to deposit the earlier one into the binding line. Only return the topic.
Cameron Belt Press and Letterpress Technology in Book Printing