calculating a difference between the known volume of the cavity and {HEAD ~ the measured volume} of discharged fluid into the cavity to determine the volume of {TAIL ~ the persons body} 
calculating a difference between the known volume of the cavity and { HEAD ~ the measured volume } of discharged fluid into the cavity to determine the volume of { TAIL ~ the persons body }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL