To determine which printing your USB book is from, open your book to the copyright page.  On the very bottom of the page, it will say “Printed in the United States of America” followed by a series of numbers:

10  9  8  7  6  5  4  3  2  1

The printing is the number that appears on the right.  For instance, the numbers above indicate that the book is in its first printing.

If the numbers appear as:

10  9  8  7  6  5  4  3  2 

The book is in its second printing, and so on.