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