| http://www.w3.org/ns/prov#value | - In the illustrated embodiment of FIG. 4, for example, the position sensor 79, 81 comprises a light source 79 emitting a laser or other beam of light across the conveyor 22 to a reflector 81, which reflects the beam of light back to a photocell 81 (which may or may not be associated with the light source 79).
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