Codabar was developed in 1972 by Pitney Bowes, Inc. It is a discrete, self-checking symbology that may encode 16 different characters, plus an additional 4 start/stop characters. This symbology is used by U.S. blood banks, photo labs, and on FedEx airbills.

Since Codabar is self-checking, there is no established checksum digit. Should a specific application wish to implement a checksum digit for additional security, it is up to the implementer to define and handle same. However, keep in mind that other applications that read your barcode will interpret your checksum digit as part of the message itself.

Codabar is also known as Ames Code, USD-4, NW-7 or 2 of 7 Code.

A Code 11 Barcode has the following structure:

1. One of four possible start characters (A, B, C, or D), encoded from the table below.
2. A narrow, inter-character space.
3. The data of the message, encoded from the table below, with a narrow inter-character space between each character.
4. One of four possible stop characters (A, B, C, or D), encoded from the table below.

In the following text, we will discuss the encoding of the barcode by considering that the number "1" represents a "dark" or "bar" section of the barcode whereas a "0" represents a "light" or "space" section of the barcode. Thus the numbers 1101 represents a double-wide bar (11), followed by a single-wide space (0), followed by a single-wide bar (1).