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Code39 is one of the most widely used barcode symbologies. However, Code39 accepts only 43 different characters as valid input.
To encode all ASCII characters, people designed extended Code39 on top of code39. Extended Code39 barcodes
use two code39 characters to represent a special character. Therefore, an extended code39 barcode is usually longer than a regular code39 barcode.
Extended Code39 is self-checking. A check digit is optional.