Interleaved 2 of 5

Interleaved 2 of 5 is a continuous two-width barcode symbology encoding digits. It is used on cartons of products, while the products inside are labeled with UPC or EAN.

I2/5 encodes pairs of digits; the first digit is encoded in the bars, while the second digit is encoded in the spaces interleaved with them. The digits are encoded as follows:
0 NNWWN
1 WNNNW
2 NWNNW
3 WWNNN
4 NNWNW
5 WNWNN
6 NWWNN
7 NNNWW
8 WNNWN
9 NWNWN
The start bars are NNNN; the stop bars are WNN.

Sometimes an odd number of digits is encoded by putting five narrow spaces in the last pair, but more commonly a checksum is appended.