Dewey (DDC)

Let's look at the following example to illustrate:

The book Mechanics of fatigue by Vladimir V. Bolotin is located on the shelf at 620.1126 BOL.

This number, 620.1126 BOL, is the call number (shelf number) which can be found on the spine (back) of the book.

Let's look at the number 620.1126 BOL by breaking it down:

620	This part of the number indicates the main class number, consisting of three digits. In this case the 620 is the main class for Mechanical Engineering.
.	The main class number is followed by a decimal point.
1126	The decimal point is followed by numbers to indicate sub-divisions of the main class.
BOL	The sub-division number is followed by three alphabetical letters (normally the first three letters of the author's name or the title of the book). In this case BOL = Bolotin (the author's surname).

Make sure you understand the order of books with such numbers:

Note: Sometimes there are codes before the actual number, e.g. REF, OS, GB, etc. These indicate collections or branches.

Dewey Decimal Classification (DDC)