However, in the presence of environmental inputs, both Km and Ks change, and the relationship between X0 and Ei can be affected greatly.
Therefore, it becomes difficult or impossible to calculate Ei from the measured value of X0.
Consider now what happens if the system is converted into a high-gain, closed-loop one, as shown in Figure 3.4, by adding an amplifier of gain constant Ka and a feedback device with gain constant Kf.