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