Take the following transfer function of a 3rd order system:
Pole Damping Frequency Time Constant (rad/seconds) (seconds) -1.13e-01 1.00e+00 1.13e-01 8.89e+00 -3.13e-01 + 1.75e+00i 1.76e-01 1.78e+00 3.19e+00 -3.13e-01 - 1.75e+00i 1.76e-01 1.78e+00 3.19e+00
and with the following unitary step response:
If I compute the percentage overshoot (PO) based on the damping ratio $\zeta=0.176$, I get:
However, if I compute the PO using the graphical method (comparing the peak value with the final value) I get a completely different result:
I don't understand why such discrepancy. Why are my PO computations not matching?