A plurality of mass gas flow controllers are arranged to control {TAIL ~ flow} into {HEAD ~ a respective inlet port} 
A plurality of mass gas flow controllers are arranged to control { TAIL ~ flow } into { HEAD ~ a respective inlet port }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD