Codabar (also known as Codeabar, Ames Code, NW-7, Monarch, Code 2 of 7, Rationalized Codabar, ANSI/AIM BC3-1995 and USD-4) is a relatively old (invented in 1972) linear barcode. It encodes digits, arithmetic operations (+-*/), colon (:), dollar symbol ($) and letters A to D. in some specifications, E, N, asterisk, and T are used in matching pairs to mark the beginning and end of the code. As of 2010, Codabar is still in use.
Codabar can be accurately read even when printed on dot-matrix printers. While not as dense as newer barcodes, Codabar has a large installed base in libraries. It is even possible to print Codabar codes using typewriter-like impact printers, which create a large number of codes with subsequent numbers without any digital equipment. After each printed code, the printer's stamp is mechanically turned to the next number, as for example in mechanical mile counters.
This code is essentially a kind of alphabet that directly converts symbols into barcode fragments. The table, how every symbol is converted to barcode fragment, is given below. Depending on the particular specification, Codabar can represent multiple digits. Some specifications define additional symbols but they do not cover complete alphabet. There is no standard check digit.
Each character comprises 7 binary identifiers (4 bars and 3 spaces). Each identifier or element is made up of a certain multiple of constant-width modules. Different specifications allow for different width modules, the smallest being 0.0065 inches, allowing 11 characters per inch to be encoded. Logical 0s and 1s are represented by narrow and wide elements respectively.
|A or T||ll l l||0100||011|
|B or N||l l ll||0001||110|
|C or *||ll l l||0001||011|
|D or E||ll l l||0010||011|
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