That bar code on your cereal box holds information read by a laser scanner. It's not much information, but it's enough to let the supermarket take your money, keep track of inventory, follow trends in customer preference, and restock its shelves. Scanners and bar codes speed up checkout, but they've got a few limitations. The scanning laser needs a direct line of sight to the bar code, and the bar code itself needs to be reasonably clean and undamaged – one reason your cashier might have to swipe that bag of spuds four or five times before the scanner reads it.
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