This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
When a book is laid on a table for reading the pages at the beginning or end, it will not stay open flat on account of the difference in the thickness of the open parts. One person, doing a great deal of reading, uses a small card, with the corner cut out, which is placed under the side of the book having the smallest number of leaves, as shown.
Ill: Some Conventional Designs for Cardcases