where ∆t is the time after calibration with pHcal, and ∆T is the difference of the temperature with respect to Tcal=37°C. In addition a factor S*0.0147, which is the same for all ISFETs, is taken into account for correction of the temperature sensitivity of the blood pH itself.
In order to measure the actual blood temperature necessary to solve eqn. 37, the ISFET chip contains a temperature-sensitive resistor which is also characterised beforehand; the data from this resistor are also stored in the PROM connector.