{TAIL ~ The first position} is used by {HEAD ~ apparatus} 10 when a background or reference reading is desired 
{ TAIL ~ The first position } is used by { HEAD ~ apparatus } 10 when a background or reference reading is desired
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH