the density determination system is operable to determine a first density value and {HEAD ~ a second density value} of {TAIL ~ the fluid} at the first time and the second time, respectively 
of
the density determination system is operable to determine a first density value and { HEAD ~ a second density value } of { TAIL ~ the fluid } at the first time and the second time , respectively
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH