Ever suspected a supermarket has charged you twice for one item? You may be right. Some checkout systems can indeed scan a barcode more than once, admits scanner maker PSC Scanning of Oregon. The problem tends to occur in checkouts with a built-in barcode scanner.
As the cashier moves a bag of apples, say, onto the conveyor, loose folds of semi-transparent cellophane packaging can momentarily get in the way of the scan. This can make the device recognise it twice 鈥� and charge you double. The solution is a timer (US 2003/10824). Once the scanner has recognised a barcode, it cannot scan anything else for a few seconds or so. So the risk of a second scan of the same thing is much reduced.
