The 1D Add 2 barcode format adds two digits to the end of EAN 13, EAN 8, or UPC-A barcodes covered by the GS-1 framework. Printed just to the right of the original barcode, Add 2 codes are strictly limited in the format and amount of data they can encode. These codes don’t contain a digit check and can’t be used independently. They must be used in conjunction with supported barcode formats to be accurately read by scanners.
For this reason, both the Add 2 and Add 5 formats are considered supplementary codes; while they can contain critical data that provides a unique identifier, they can’t function in isolation. This makes them ideal for cases where companies have large amounts of similar objects — such as books or manuscripts — that still require unique identification.