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