A system includes one or more electrochemical sensors. The system includes an outer catheter having an inner liner extending past the end of the outer catheter and an inner catheter disposed within the outer catheter. A pressure of the combined flow at a location downstream from the first inlet and the second inlet is monitored. The downhole flow control means of the zone isolating and testing apparatus comprises two valves, one for closing off the annulus between the inner tube and outer tube of the concentric drill string and the other for closing off the inner space of the inner tube. The invention relates to a heat exchanger and to the use thereof. An algorithm associated with the rule and included in the rule definition file is executed to provide the requested value.