Each barcode is a 14-digit numeral. There are actually 13 digits in the data stream: the 14th is a check digit. The first digit is simply a flag indicating whether or not the barcode is part of a composite barcode. When used as intended, to encode identification numbers, the second digit is an indicator digit used to show things like level of packaging. (There is no explicit application identifier and it is not entered in the data stream, but "01" is implied.)
For the basic GS1 DataBar Omnidirectional symbology, each barcode has 46 bars and spaces in a total of 96 modules. (A "module" is the minimum unit of width measurement. In GS1 DataBar it is the same as the X-dimension.) The height is at least 33 modules. Each barcode begins and ends with two one-module wide guard bars, either a bar-space or a space-bar pattern.
There are four symbol characters in each barcode with a finder pattern between the left pair and another between the right pair. The symbol characters in each pair are always read beginning with the character to the outside of the finder pattern. Hence, the sequence of symbol characters is 1st, 2nd, 4th, 3rd.
The elements within each character are always read toward the finder pattern, so the 2nd and 3rd characters are read from right to left. The outside characters (1st and 3rd) are 16 modules wide with 4 bars and 4 spaces. The inside characters (2nd and 4th) are 15 modules wide with 4 bars and 4 spaces. The finder patterns are each 15 modules wide. The first has 3 spaces and 2 bars. The second has 2 spaces and 3 bars. The finder patterns express the mod 79 checksum.
The Character Set
