1-7 CRITERIA OF GOOD CONTROLTo evaluate a control system effectively, two decisions must be made: (l) the test must be specified, and (2) the criteria of good control must be selected. A step change in setpoint or load is the most common test. A typical step response test is illustrated in Figure 1.10a. The three most common criteria of good control are: quarter amplitude decay, integral of absolute error, and critical damping. A discussion of each criterion follows.