Universal Product Code
UPC (Universal Product Code) was the original barcode symbology widely used in America for items in stores. The first item to ever be placed under a UPC scanner in a retail environment was a 10-pack of Wrigley's Juicy Fruit chewing gum at Marsh's supermarket in Troy, Ohio, June 24, 1974.Nowadays the UPC is being replaced by EAN.UCC-12, that encodes twelve digits as follows:
SLLLLLLMRRRRRRE
where S and E are the bit pattern 101, M is the bit pattern 01010, and L and R are digits, seven bits long each. This is a total of 95 bits.
The first L digit is 0 for ordinary items, 3 for pharmaceuticals, 2 for random-weight items, and 5 for coupons. The rest of L is the manufacturer code. The first five R digits are the product code assigned by the manufacturer. The last digit is a redundancy check.
Each digit has four forms, of which two are used in UPC-A and three in EAN. For 6, the forms are:
0101111 (L)
0000101 (L in EAN)
1010000 (R)
1111010 (unused)
The codes for the ten digits are:
0 0001101
1 0011001
2 0010011
3 0111101
4 0100011
5 0110001
6 0101111
7 0111011
8 0110111
9 0001011
Company prefixes are assigned by EAN-UCC.
In the barcode, each number is represented by two bar and space configurations. One configuration is used in the "L" digits, while another is used in the "R" digits. This is done so that the barcode can be scanned forwards or backwards, and the scanner recognizes from the barcode form which direction the code is being scanned so that it can be registered correctly. If it were not for this, products could easily be registered incorrectly.