The first six digits of the UPC are the vendor��s unique identification number. All of the products that one vendor sells will have the same first six digits in their UPCs. The next five digits are the product��s unique reference number that identifies the product within any one vendor��s line of products. The last number is called the check digit that is used to verify that the UPC for that specific product is correct.
The check digit verification works like this, using the UPC 438571639853 as an example:
- The digits in the odd positions are added together: 4 + 8 + 7 + 6 + 9 + 5 = 39
- That number is multiplied by 3: 39 x 3 = 117
- The digits in the even positions (except for the 12th digit) are added together: 3 + 5 + 1 + 3 + 8 = 20
- This sum is added to the value in step 2: 117 + 20 = 137
- The check digit is the number that when added to that sum - 137 - equals a multiple of 10: 137 + 3 = 140, therefore the check digit for the above UPC is 3, which appears as the last digit of the UPC.
Each time that a UPC is read, typically by a scanner reading the bar code, this calculation is done. If the check digit is different than the one that is calculated, then the computer knows that there is something wong with the UPC.
Anyone wishing to use the UPC system must first apply for the rights through the Uniform Code Council.
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