How do barcodes work?

Barcodes are a machine-readable way of writing letters and
numbers. A laser is shone onto the barcode and the refl ected
light can be interpreted by the barcode reader. There are
many types of barcodes, but the ones most commonly found in
supermarkets use a row of lines of diff erent widths. The diff erent
widths represent diff erent numbers. In the UK many items are
coded with a GTIN – Global Trade Item Number. This allows
the manufacturer to print the barcode on the packages. The
numbers are unique to that item. The barcode only has a
number, but no product information. That is held in a database
which the retailer can access at the point of sale. It also means
that shops can set their own prices and change them easily.