New physical principles are used to determine the number of inventory goods on a store's display shelves. One principle involves transmitting waves (mechanical, sound or ultrasound) thru an unknown number of goods resting on an insulated plate. Another principle to determine the unknown mass is the inertial...http://www.google.de/patents/US5654508?utm_source=gb-gplus-sharePatent US5654508 - Method of determining a store's physical inventory
