{TAIL ~ The pressure} in the tube is then reduced to {HEAD ~ below 500 millitorr} but not less than 150 millitorr 
{ TAIL ~ The pressure } in the tube is then reduced to { HEAD ~ below 500 millitorr } but not less than 150 millitorr
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH