A Universal Price Code is represented by a bar code that can be scanned at the point of purchase. A UPC consists of a six-or nine-digit company prefix, a five- or two-digit product number and a check digit. A specific algorithm determines the last number, which is used to confirm the accuracy of the first 11 digits. A UPC can be validated with a manual calculation that can be checked at a UPC-validation website.

Write down a UPC. For example, 796030114977 is the UPC of a product. The last number is the check digit.

Sum the digits in the odd positions, starting at the left. In this case you have 7 + 6 + 3 + 1 + 4 + 7 = 28.

Multiply the answer in Step 2 by 3. The result is 84.

Sum the numbers in the even positions, ignoring the last (12th) digit because that is the check digit that you are verifying: 9 + 0 + 0 + 1 + 9 = 19. Do not multiply this number by 3.

Add the results from Steps 3 and 4: 84 + 19 = 103.

Subtract the number in Step 5 from the next higher multiple of 10. In this example, the next multiple of 10 after 103 is 110, so subtract 103 from 110: 110 minus 103 = 7. This is the check digit in the UPC in Step 1, so it is verified.

Enter the 12-digit UPC at a validation site like the Universal Product Code (UPC) Validation site and click on the "Validate" button. In this example, enter 796030114977, click on the button and see the message, â€œUniversal Product Code (UPC) '796030114977' is valid."