Code 39
Self-checking encoding distinguishes Code 39: each character is drawn as nine elements of which exactly three are wide, so an error inside a single character is detectable without any check digit. David Allais and Ray Stevens developed the symbology at Intermec in 1974, the first to carry a full alphabetic range covering A through Z, the digits 0 through 9, and the punctuation set - . $ / + % and space. Density is the price of that redundancy. At a 0.19 mm X-dimension a Code 39 symbol is materially wider than a Code 128 symbol holding the same string, and practical payloads stop near eighty characters. Quiet zones of ten modules are required on both sides. United States defence, automotive, and healthcare labelling standards adopted it early, and use in those sectors outlived its density disadvantage.
The first barcode symbology capable of encoding the full alphanumeric character set (A-Z, 0-9, plus special characters). Code 39 is self-checking — each character can be verified independently — making it popular in US defense, automotive, and healthcare applications where reliability outweighs density.
Code 39
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