A theorem relating the integrated square of the impulse and step response of a two terminal-pair network to its input impedance is developed; this theorem is in a sense the time domain equivalent to the gain-bandwidth relationship in steady state. As an application, a simple method is presented for evaluating the integrated square,
![\\int_{0}^{\\infty } [r(t)-r_{ss}]^2 dt](/images/tex/11642.gif)
, of the difference between a signal

and its steady state value

; the method is based on Darlington\´s procedure for determining a reactive network from its transfer function.