When an abnormal operation occurs in the production line, it is thus easy to find which {HEAD ~ working group} is in {TAIL ~ trouble} 
When an abnormal operation occurs in the production line , it is thus easy to find which { HEAD ~ working group } is in { TAIL ~ trouble }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL