EAN-13 and UPC-A — check digit calculated automatically
The barcode was invented in 1952 by Norman Joseph Woodland and Bernard Silver, but it took over two decades for retailers to adopt it. The breakthrough came on June 26, 1974, when a 10-pack of Wrigley's chewing gum became the first retail product ever scanned at a checkout, at a supermarket in Troy, Ohio, using the newly standardized Universal Product Code (UPC). Europe followed a few years later with its own compatible standard, the European Article Number (EAN), now known internationally as GS1's EAN-13 and UPC-A symbologies.
Both formats encode a product number as a sequence of black bars of varying width, readable by a laser or camera scanner from almost any angle. The final digit is always a check digit, calculated from the others using a fixed weighting formula — this lets a scanner instantly detect a misread or damaged barcode rather than ringing up the wrong item, which is why it's calculated automatically here rather than typed in by hand.
EAN-13 is the standard used across Europe, Russia and most of the world for retail packaging, while UPC-A remains common in the United States and Canada — the two are technically compatible, since a UPC-A number is simply an EAN-13 number with a leading zero. Together they appear on the vast majority of packaged products sold anywhere today.