Let’s illustrate with the following book:

781.97 W832

Secular music in America, 1801-1925 Wolfe, Richard J.

The first line of the call number, 781.97, represents the subject of the book and each number has a meaning.

The first number, 7, puts the book in the 700s which is Fine Arts. 

Adding the second number, 8, puts the book in the 780s which is music.

The remaining numbers on the first line represent the sub-division under music.

Read the first line as a whole number with a decimal number.

The second line, beginning with the first letter of the author’s last name, identifies the author.