the pressure determination system is operable to determine {HEAD ~ the pressure values} by determining a first pressure value and {TAIL ~ a second pressure value} of the fluid at a first time and a second time, respectively, during the oscillation of the pressure, and 
by determining
the pressure determination system is operable to determine { HEAD ~ the pressure values } by determining a first pressure value and { TAIL ~ a second pressure value } of the fluid at a first time and a second time , respectively , during the oscillation of the pressure , and
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH