Interleaved 2 of 5 barcodes begin with the start pattern of a narrow bar, narrow space, narrow bar, narrow space. They end with a wide bar, narrow space, narrow bar.

Here is a table of wide & narrow combinations for each of the 10 digits:

0: nnwwn
1: wnnnw
2: nwnnw
3: wwnnn
4: nnwnw
5: wnwnn
6: nwwnn
7: nnnww
8: wnnwn
9: nwnwn


If you were to encode the digits "01", designating bars with capital letters and spaces with lowercase letters, the pattern would be:
NwNnWnWnNw
As you can see, the lowercase letters spell out wnnnw, the code for 1, and the uppercase letters spell out NNWWN, the code for 0.

Putting horizontal bars, called "bearer bars," on the top and bottom of the code helps to prevent scan errors that could occur if the path of the scanner went above or below the symbol.

Note that by "odd" and "even" I mean "positionally-odd" and "positionally-even"; the odd-numbered digits are in the first, third, fifth, and so-on positions, and the evens are in the second, fourth, sixth, etc.

Odd numbers of digits can be resolved by adding a 0 to the left of the number (123 becomes 0123).

Codabar	Code 2 of 5	Code 3 of 9	Interleaved 2 of 5
Postnet	UPC	Code 128	Code 16k

Thu Jul 24 11:03:09 PDT 2008		barcode/i25.src
Updated: Thu Aug 18 2005 9:31.35		Viewed: never