Remember card catalogues? Before databases and bar code scanners? Libraries had a card for every book in their collection. They were filed in cabinets full of small drawers that pulled way out. You could look up books by title or by category. So if you were assigned to do a report on the Emancipation Proclamation, you’d find the “E” drawer and look for your key word. Once you found books with your subject, you’d write down the shelving numbers (the Dewey Decimal System) and then go look for your books, scanning the numbers on the shelves until you found the right section. Of course, the kid who sat in front of you in Civics class may have gotten the best books first, but you could usually find SOMETHING. Besides, the library also had encyclopedias that couldn’t be checked out and they were always good for some snippets of information that could form the basis of your report. When I first started in publishing, it was a value-added service to provide the card, ready for filing, with the book order. The mysterious numbers and the odd way of organizing the information is actually a language that librarians can read at a glance. Just for fun, here’s a web site where you can generate your own old-fashioned book catalogue cards: Make your own library catalogue card!