Systems and methods for reducing erroneous weighing of items such as by detecting items (11) extending beyond a periphery of a weigh platter (20, 120, 170, 240) whereby in one configuration, the system employs a light guide (30, 320) for routing a light beam to a detector (40,140) operative to detect interruption of the beam due to an item encroaching upon or overhanging an edge of the platter. In another configuration, the scale includes a perimeter gap (252, 257) between the platter outer edge and scanner housing frame or checkout counter, a light beam directed angularly upward through the gap is partially obstructed by the frame and platter whereby light exits the gap forming a light plane, wherein an object placed on the platter extending across the gap intersects the light plane thus scattering light rays, some of which are sensed by a detector (280). Various indicators (295, 297) for alerting the operator of off-scale detection are also described.