Codabar was originally developed for use in retail price-labeling systems.
However, after the National Retail Merchants Association (NRMA) selected
another symbology as their standard in 1975, Codabar was promoted for use
in a variety of non-retail applications such as libraries, shipping,
and the medical industry. However, because Codabar is not as versatile
or reliable as the other symbologies, the trend in bar code use since
the 1980s has moved from Codabar and toward the other symbologies.
The Codabar character set contains the following usable characters:
The four alphabetic characters are used only as start and stop characters, and are not used within the contents of the bar code message. Therefore, with the exception of the 6 special characters shown above, Codabar is a numbers-only symbology, like Interleaved 2-of-5.
Each Codabar character is represented by seven elements: four bars and three spaces. Of the seven elements, either two or three elements will be wide, and the rest will be narrow. The lack of a fixed number of wide elements can theoretically lower the data integrity of Codabar bar codes relative to the other symbologies.
A fourth space, an "intercharacter space," separates each bar code character from the next, but is not actually itself a part of a bar code character. The width of this space is not critical and it is often set to be identical to the width of a narrow space.
The Start and Stop Characters
Unlike the other bar code symbologies, Codabar has a number of different start and stop characters. These characters are represented by any of the four lower case letters, "a", "b", "c", and "d". Any one of these four 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 bar code need not be the same. The lack of a single accepted pattern for the start and stop characters is another factor which can theoretically lower the data integrity of Codabar.
It is common for a bar code scanner to have an option specifying whether or not the start and stop characters are to be transmitted as part of the bar code.
Lack of Check Digits
Codabar has no option for check digits. As has already been discussed, 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. This can't help but make Codabar less secure than the other bar code symbologies. Since Codabar doesn't even have the option to add check digits, there are no means available for bringing the reliability of Codabar bar codes to the same level as the other symbologies. Most bar code manufacturers recommend the use of either Code 39 or Interleaved 2-of-5 in applications where Codabar is being considered.
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