measuring the volume of discharged fluid entering {HEAD ~ the cavity} until {TAIL ~ the cavity} reaches the known volume; and 
measuring the volume of discharged fluid entering { HEAD ~ the cavity } until { TAIL ~ the cavity } reaches the known volume ; and
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH