The distance between two sensing chip 31, 32 is represented by L2, and {HEAD ~ the distance} between two light focusing means 16, 16 is represented by {TAIL ~ L1} 
is represented by
The distance between two sensing chip 31 , 32 is represented by L2 , and { HEAD ~ the distance } between two light focusing means 16 , 16 is represented by { TAIL ~ L1 }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL