UPC-A, UPC-E, and EAN-13 can all have an additional barcode located to the right of the main barcode that contains additional information. This second barcode is normally not as tall as the primary barcode and can encode either two or five additional digits. Supplement 2 encodes two digits.

Applications
UPC/EAN Extension 2 is used to encode information (such as issue number) for newspapers, books, and other periodicals.

Benefits
2-digit supplement can be used to track which issue of the magazine is being sold for sales analysis or restocking purposes.

Limitations
Since the 2-digit supplement is mostly used in conjunction with a UPC-A, UPC-E, EAN-13, or EAN-8 barcode, it makes the barcode longer and requires wider scanners. The use of the extension is limited to publication industry.

Technical Specifications
Encoding both 2-digit extension and 5-digit extensions follows the same underlying structure. A left-hand guard bars, encoded as 1011 followed by two to five data characters, each separated by a separator character, encoded as 01. There is no "stop" character. The barcode is assumed to end when a character separator (01) doesn't follow a valid character.

Additional Information
The 2-digit extension is not always the same as the "Issue Number" that is printed on the cover of books and publications. Sometimes the encoded issue number just gets incremented with each issue. In other cases, the encoded issue number may just be the number of the month of the year, or the week number, depending on the frequency with which the periodical is published.

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