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Interleaved 2-of-5 is often selected instead of Code 39 because bar
code messages that only contain numbers can be encoded in Interleaved
2-of-5 using about half the space required by Code 39.
The Character Set The Interleaved 2-of-5 character set only contains the ten digits, 0-9. However, if you only need to encode numbers, Interleaved 2-of-5 does the job in about half the space of Code 39. Although much denser than Code 39, the theoretical data security of Interleaved 2-of-5 is not quite as high. For this reason, we suggest that Interleaved 2-of-5 always be used with the Check Digit option enabled or that you standardize on a single character length of Interleaved 2-of-5 bar codes. The Symbology Structure Each Interleaved 2-of-5 character is represented by five elements: five bars or five spaces. Like Code 39, the name Interleaved 2-of-5 comes from the patterns of bars and spaces that represent the individual characters within the bar code. Each character has two wide and three narrow elements. With Interleaved 2-of-5, characters are represented in pairs. In each 10 elements, the five bars represent one character and the five spaces in between them represent the next character. All Interleaved 2-of-5 bar code messages must contain an even number of digits. Therefore, a leading zero will be added to the front of the Interleaved 2-of-5 bar code message in either of the following two situations: Unlike Code 39, Interleaved 2-of-5 contains no intercharacter spaces. However, Interleaved 2-of-5 does have start and stop characters. The Start and Stop Characters Unlike the Code 39 asterisk which is used as the start and stop character at each end of the bar code, the Interleaved 2-of-5 start and stop characters are different from each other. They are also shorter than the standard character length in the symbology and no particular character (like the asterisk in Code 39) is associated with them. From left to right, the start character is: narrow bar narrow space narrow bar narrow space From left to right, the stop character is: fat bar narrow space narrow bar Bearer Bars 
Interleaved 2-of-5 bar codes can, optionally, include bearer bars
either as a rectangular frame around the bar code or as two perpendicular
bars across the top and bottom of the data-expressing bars.
The term "bearer bars" originates with the manufacture of metal grates: The bearer bars in a grate bear weight and run perpendicular to the trans bars (which connect the bearer bars). When bar codes are printed directly on corrugated cardboard boxes, flexible rubber printing plates are used. These plates often bend when they make contact with the cardboard, resulting in a distorted bar code. To prevent this bending, box printers stiffen the plates by adding bars perpendicular to the data-expressing bars. A side-effect of stiffening the plates in this way is that the images of these additional bars are added to the printed bar code. By analogy with the bearer bars in metal grates, which run perpendicular to the trans bars, the additional bars in the bar code have come to be called "bearer bars" as well. A secondary purpose has been found for bearer bars: if a bar code reader passes over the bar code at too sharp an angle, there is a danger that it will not read data-expressing bars at the ends of the bar code. Since bearer bars can be used to prevent this, they are sometimes included even on bar codes that are being printed on a plain label with a label printer. |
