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