(En español)

Laser beams can decode bar codes up to 500 times a second. The computer can translate the symbol in less than 1 second. Humans, with a lot of patience, can decode them too.

We are going to show you just what the UPCA code means and how to decode it.

What a UPCA code means

If you were a cash register or scanner, the center of your universe is Dayton, Ohio - home of the Uniform Code Council. The people at the UCC are dedicated to spreading the Universal Product Code. The most common version of this code is called the UPCA.

The first six (6) digits identify the manufacturer. All of the products they make will begin with the same six digits. This number is assigned by the UCC. The second (5) digits are the item identification given to that product by the manufacturer. This allows them 99,999 products that they can make. There is no need for this number to reflect or become a model number. The 12th digit is a check digit.

How to decode a UPCA

There are twelve digits that make up the UPCA code. Each digit is represented by a seven bit binary code.

Use the code key, and if the binary code is 1 then it is represented by a black line. The 0 (zero) is a space (white).

Code Key

There is a center code of five (5) lines, which are the digits 01010 which bisects the symbol.

On the left-hand side of the center code, use the left binary code. On the right-hand of the center code switch to the right binary code. See Table 1. This mirror image coding lets the scanner read the numbers in either direction.

Table 1

Code Key Digit Left Right Value Binary Code Binary Code 0 0001101 1110010 1 0011001 1100110 2 0010011 1101100 3 0111101 1000010 4 0100011 1011100 5 0110001 1001110

The Start and End Code's are used by the scanner/computer to set the width of the binary digits within the symbol.

The check digit

The last digit is a check digit. The scanner uses an algorithm to calculate this digit. If the scanner does not calculate the correct check digit the read is rejected.

You can calculate the last digit of a UPCA code. Use the "human readable numbers" from any 12-digit code.

1. Add the sum of the odd-spaced digits (1st,3rd,5th,7th,9th,11th). Multiply the sum by 3.
2. Add up the even-spaced digits (don't include the check digit).
3. Add the answers from #1 and #2.
4. The check digit is the number that you would have to add to get to the next multiple of 10.

Bar codes are not just a meaningless collection of lines that only a computer can understand. With a little patience and a little practice, you to can decode the bar code!