The performance criteria that are used to characterize the transient response to a unit
step input include rise time, peak time, overshoot, and settling time.We define the rise
time tr as the time required for the response to rise from 10 percent of the final value
to 90 percent of the final value. The time to reach the peak value is tp. The swiftness of
the response is measured by tr and tp. The similarity with which the actual response
matches the step input is measured by the percent overshoot and settling time ts. For
underdamped systems the percent overshoot P.O. is defined as