(Solved by Humans)-In general, the process transfer function parameters will not be

Question

In general, the process transfer function parameters will not be constant, since environmental and/or operational factors may be significant (e.g. changes in ambient temperature / pressure, changes in the mass of the melt in, say, a temperature control process). Assess how ?20% variations from nominal in the actual process transfer function parameters affect the system's unit step response.

(i.e. the SPC assumes the process TF is as given above, but the actual process parameters change, so that the denominator time constants and the

4-second time delay may vary from their nominal values by ?20%. Take these variations one-at-a-time.)???????????????????????