Codabar

Although newer symbologies hold more information in a smaller space, Codabar has a large installed base in libraries.

For purely numerical data, such as the library barcode pictured above, the Luhn algorithm is popular.

"Rationalized codabar" uses a fixed ratio and allows the character widths to vary.

Some variants allow the symbols dollar, dash, plus sign, colon, slash, and dot.

For example, the library barcode illustrated begins with A and ends with B. FedEx tracking number barcodes, on the other hand, begin with B and end with D. Although there are 12 combinations of one wide bar (four choices) and two wide spaces (three choices), the start/stop codes are limited in two ways: