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Bar Codes in Action

Bar codes incorporate high-tech number generation and tracking.

The bar code, invented in the 1940s by Ben Silver and John Woodland, is a series of numbers and dashes. The dashes are read by a machine. The 12-digit number can be read by people.

Bar codes have a UPC number. UPC stands for Universal Product Code. Product makers apply to the Uniform Code Council for permission to get a UPC number, which requires an annual fee. The UCC then assigns a six-digit number to each manufacturer.

The next five numbers in the 12-digit bar code correspond to a particular item. Even different sizes of the same product (a 12-ounce can of vegetables versus a 16-ounce can of the same vegetables) have unique bar codes.

The last digit is a "check digit," which prompts the scanning machine to run a "check" to see that the item was scanned correctly. If the scan returns a different number from the one assigned to the item, then the scanner returns a negative scan and human intervention is required.

To find the "check digit" in a 12-digit UPC bar code, do the following:

  1. Add the odd-numbered digits to get a.
  2. Multiply that sum by 3 to get b (a times 3).
  3. Add the even-numbered digits to get c.
  4. Add c to b to get d.
  5. Find the next higher multiple of 10 (e).
  6. Subtract e from d. The answer is f.

For example, take the number 111111111111.

  1. a = 6
  2. b (a times 3) = 18
  3. c = 5
  4. d = 23
  5. 30 is the next multiple of 10. e = 30
  6. 30 23 = 7.

So, f, the check digit is 7.

The machine reader doesn't need the numerals, though. It scans the space between the bars in order to get the code.

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