From the original text:
The Histomap of Evolution: earth, life and mankind for ten thousand million years. Arranged by John B. Sparks. Copyright, 1932, by John Sparks, 1942 edition. Printed and distributed in U.S.A. by Rand McNally & co. One dollar.
1. Locate the little slider bar with the minus sign at one end and the plus sign at the other. Here it is shown on some yellow-with-text background:
Click on either end, or use the slider, to increase/decrease magnification level.
2. Use your mouse—click and hold and move—to reposition the map.
Note that this map is just one of approximately 60,000 digital maps that have been created from the collection's total supply of over 160,000 historical maps. Unbelievable.