…detect light reflected from striped bar codes on packages, decode the symbol, and relay the information to a computer so that it can add the price to the bill.

The numbers represented by a barcode are also printed out at its base.

…most checkout counters include a bar-code scanner, which reads into the computer the Universal Product Code (UPC) printed on each package. Cash register receipts then include brief descriptions of the items purchased (by fetching them from the computer database), and the purchase information is also relayed back to the computer…