This double-checking could catch errors resulting from erroneous keying or reading. Now, with computerized cash registers, we do not see any double-checking. This may come from pressure to process as many transactions as quickly as possible. Maybe managers ignore the possibility of error or they build a certain percentage of the cost into the sale price to cover losses of this type. This translates into higher costs for consumers.
Humans are fallible.
They have short attention spans. Eyes misread numbers and fingers hit wrong keys. Undetected keying errors result in overcharging customers or lost revenue to merchants. Many stores have installed optical scanning devices to eliminate such problems and to save labor costs. Overcharging Unwary Consumers Consumer associations and labor unions see disadvantages in laser scanning and bar codes.