An acoustic velocity meter is arranged to supply to an analyzer {HEAD ~ a signal} indicative of {TAIL ~ an acoustic velocity} within the mixture of reference gas and gaseous substance in the chamber 
indicative of
An acoustic velocity meter is arranged to supply to an analyzer { HEAD ~ a signal } indicative of { TAIL ~ an acoustic velocity } within the mixture of reference gas and gaseous substance in the chamber
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH