Optical code scanners are used in point of sale (POS) terminals to read optical codes on items which are presented to the POS terminals for purchase as part of a purchase transaction. Integrated into some of the optical code scanners are weigh scales that are used to weigh items sold by weight. To maintain scale accuracy, a zero function is periodically performed by the scale, usually at the request of an operator. The zero function causes the weigh scale to determine the weight of the elements or structures that are part of the weigh scale and attached to the weight determining elements of the weigh scale. The determined weight becomes the zero weight for the weigh scale after each zero function is performed. The weigh scale determines the net weight of an item placed on the weigh scale by measuring the gross weight which includes the weight of the item and the elements and structures attached to the weight determining elements and then subtracting the zero weight.
The zero function should not be performed when any foreign item or material is present on the weigh scale as this would cause an improper zero weight to be set which would cause any subsequent determined weight for items to be inaccurate. Thus, an operator must determine that the proper conditions exist before causing the weigh scale to perform a zero function. This requires training for the operator.