However, Code 39 is still used by some postal services (although the Universal Postal Union recommends using Code 128 in all cases ), and can be decoded with virtually any barcode reader. This means that very small goods cannot be labeled with a Code 39 based barcode. Possibly the most serious drawback of Code 39 is its low data density: It requires more space to encode data in Code 39 than, for example, in Code 128. The barcode itself does not contain a check digit (in contrast to-for instance- Code 128), but it can be considered self-checking on the grounds that a single erroneously interpreted bar cannot generate another valid character. The width ratio between narrow and wide is not critical, and may be chosen between 1:2 and 1:3. Three of the nine elements in each character are wide (binary value 1), and six elements are narrow (binary value 0). Each character is composed of nine elements: five bars and four spaces. An additional character (denoted '*') is used for both start and stop delimiters. The Code 39 specification defines 43 characters, consisting of uppercase letters (A through Z), numeric digits (0 through 9) and a number of special characters (. Code 39 (also known as Alpha39, Code 3 of 9, Code 3/9, Type 39, USS Code 39, or USD-3) is a variable length, discrete barcode symbology.
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