The presence of {TAIL ~ the gap} 602 and {HEAD ~ the absence} of a gap 601 indicates that replacement of the consumable part 605 is necessary 
The presence of { TAIL ~ the gap } 602 and { HEAD ~ the absence } of a gap 601 indicates that replacement of the consumable part 605 is necessary
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH