The symbol comprises the following elements:

• Leading quiet zone

• Start character

• Symbol characters that represent data (including an optional check digit)

• Stop character

• Trailing quiet zone

Symbol characters: Each Codabar character is represented by seven elements: four bars and three spaces. Of the seven elements, either two or three elements are wide, and the rest are narrow. The lack of a fixed number of wide elements can theoretically lower the data integrity of Codabar barcodes relative to the other symbologies.

A fourth space, called an "intercharacter space," separates each barcode character from the next but is not itself a part of a barcode character. The width of this space is not critical and it is often set to be identical to the width of a narrow space.

Start and stop characters: Codabar has four start and stop characters, which are represented by the letters A, B, C, and D. Any of these letters can be used as a start character, and any can be used as a stop character. The start and stop characters in any given barcode need not be the same. The lack of a single accepted pattern for the start and stop characters is another factor that can theoretically lower the data integrity of Codabar.

It is common for a barcode scanner to have an option to specify whether the start and stop characters are to be transmitted as part of the barcode.

This symbology supports the following characters:

• All numeric digits (0-9)

• The following special characters:

  • Hyphen (-)

  • Dollar sign ($)

  • Colon (:)

  • Slash mark (/)

  • Period (.)

  • Plus sign (+)

• Four alphabetic characters: A, B, C, and D

The four alphabetic characters are used only as start and stop characters and are not used within the contents of the barcode message. Therefore, with the exception of the six special characters, Codabar is a numeric-only symbology, like Interleaved 2 of 5.

Codabar can contain an optional check digit that is based on the modulo 16 (mod 16) algorithm. This digit appears just before the stop character.

Because Codabar does not have a fixed number of wide spaces per character, nor does it have a set pattern for the start and stop characters, it is less secure than other symbologies. Most barcode manufacturers recommend the use of either Code 39 - Full ASCII or Interleaved 2 of 5 in applications where Codabar is being considered.

Codabar cannot represent data as densely as Interleaved 2 of 5 can. Additionally, Codabar is not much more dense than Code 39, which has the significant advantage of being able to represent the full ASCII character set. This is one of the reasons why Interleaved 2 of 5 is recommended instead of Codabar in applications where only numeric information must be encoded.

The recommended minimum symbol height for manual scanning is 5.0 mm or 15 percent of the symbol width (excluding quiet zones), whichever is greater. The quiet zones must be at least 10X wide, where "X" is the current X dimension.

Traditional Codabar: The original version of Codabar is now called Traditional Codabar. It differs from Codabar in the start and stop characters and density tolerances.

ABC Codabar: Codabar symbols can be concatenated. When this is done, the variation is known as ABC Codabar. In this variation, the D stop character in one symbol is used to indicate that the symbol should be concatenated with the data from an adjacent symbol that has a D start character. The number of labels that can be concatenated in this way is limited only by the range of the barcode scanner.