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