What is a barcode?

The two common retail barcode systems differ mainly in length. A UPC-A has 12 digits and is used widely in the United States and Canada. An EAN-13 has 13 digits and is used in most of the rest of the world. A UPC-A is simply an EAN-13 with a zero added at the front, so scanners and software treat them as the same number. Both are managed through GS1, the standards body that issues company prefixes to manufacturers.

Caribbean shops see both. Imported goods from North America usually carry a UPC, and goods from Europe, Asia and elsewhere usually carry an EAN.

The digits identify the maker and the product. The last digit is a check digit, calculated from the others so a scanner can tell when it has misread a number. Take the UPC 036000291452. Add the digits in odd positions (0, 6, 0, 2, 1, 5), which gives 14, and multiply by 3 to get 42. Add the digits in even positions (3, 0, 0, 9, 4), which gives 16. The total is 58. The number needed to reach the next multiple of ten is 2, which is the final digit. If a scan produces a different last digit, the read is rejected.

Scanning is faster than typing and removes spelling and wrong-item errors. A shop serving 150 customers a day who each buy four items scans 600 items. Saving even a few seconds per item adds up to real minutes at a busy counter. Barcodes also make stock counts quicker, because you scan the product instead of searching for it.

• A case and a single unit have different barcodes. If you buy by the case and sell by the unit, you need to decide which one you track.
• Barcodes only identify a product. They do not carry the price. The price lives in your system.
• Not everything has one. Fresh goods, repacked items and local products often have none, so you need another way to find them.

Shopkeepa scans barcodes with a phone camera, a Bluetooth scanner or a USB scanner. A scan finds products already in your own list. It does not look up names from an outside database, so you add a product once and from then on a scan finds it. See barcode scanning for the full picture.