A method and a device for indicating the presence of an object in a measuring zone (E), and for objects having a measurable cross-sectional shape, also the extent of the object along a reference line (R). The method and device makes use of lines (A, B) of radiation emitters (11) and radiation receivers...http://www.google.com/patents/US4555633?utm_source=gb-gplus-sharePatent US4555633 - Photoelectric dimension measuring system
