Four of {TAIL ~ the optical signals} from two of the inspection regions are paired for {HEAD ~ input} into one of the optical cameras and recorded on a singular frame 
Four of { TAIL ~ the optical signals } from two of the inspection regions are paired for { HEAD ~ input } into one of the optical cameras and recorded on a singular frame
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH