Also called the Industry 2 of 5 barcode or simply Code 2 of 5, the Industrial 2 of 5 symbology has been in use since the late 1960s to encode information for airline tickets and warehouse sorting systems. All information contained in this barcode is stored in the bars themselves — the white spaces are only used for separation. As a result, this code is considered inefficient when compared to newer symbologies but remains popular thanks to existing infrastructure built specifically to read these codes.
To encode information, five bars are used for each character. Two are wide and three are narrow, giving rise to the name “2 of 5”. Unlike more recent barcode formats, Industrial 2 of 5 only supports numeric characters 0-9.