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