The Universal Product Code (UPC), sometimes referred to as a bar code, is a product description code designed to be read by a computerized scanner at the cash register. The UPC permits fast checkout at the point of sale and also gives the store owner an easy method to track sales and monitor inventory.

The UPC consists of 12 numbers in groups of “0” s (dark strips) and “1” s (white strips).  The width of the strips matters. A bar is thin if it has only one strip, and thicker if there are two or more strips that are side by side. A big advantage of the UPC is that there is no letters or numbers, only the scannable strip of black bars and white spaces.
The first number is a description of the product. The next five numbers describe the product’s manufacturer. The following five numbers describes the product itself, such as size, weight, color, or some other distinguishing characteristic.

The last number is a check digit that is used to inform the scanner if there is an error in the other numbers. The preceding 11 digits, when added, multiplied, or subtracted in a certain way will equal that twelfth number. If they do not, a mistake is made somewhere, perhaps a wrinkle or fold in the scanned label.

The price is never coded into the bars of the UPC. When the scanner at the checkout counter scans a package, the cash register sends the UPC number to the store’s central point of sale computer to look up the UPC number.  The central computer then sends back the actual price of the item. It is done almost instantly. The price is put into the computer by the operator. That way, stores can decide at what price to sell an item, or the store can put the item on sale.

The end strips are “guard bars”. There are “guard bars” in the middle of the UPC. Numbers on the right side of the middle guard bars are optically the inverse of the numbers on the left. This inversion enables the bar code to be scanned from left-to-right or right-to-left. The scanning software knows if the code is the correct way or backwards or upside down.

The first UPC item ever scanned was at Marsh’s Supermarket in Troy, Ohio on June 26, 1974. It was a 10-pack (50 sticks) of Wrigley’s Juicy Fruit chewing gum and the cash register rang up 67 cents. That 10 pack Juicy Fruit gum is on display at the Smithsonian National Museum of American History in Washington, DC.

UPC scanners use a low wattage laser to read the product label. When those supermarket scanners first came out in the middle to late 1970’s, the word laser was omitted from any advertising. Lasers were associated with death rays and who wants to go to the store to be zapped by a death ray. It does take time for us to accept some new technologies.

When those new NMR (Nuclear Magnetic Resonance) machines appeared a few decades ago, people were reluctant to use them because of the word “nuclear”.  The medical profession changed the name to MRI (Magnetic Resonance Imaging) and they became acceptable.