at least two sensor means {HEAD ~ each} having {TAIL ~ a detection area} partly overlapping each other and generating an output in accordance with a detected quantity 
at least two sensor means { HEAD ~ each } having { TAIL ~ a detection area } partly overlapping each other and generating an output in accordance with a detected quantity
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH