Callendar's ‘curve distortion criterion’, Sd, and a factor, Kr, in his power gain expressions are simply related to the ‘performance factor’, n and ‘inherent performance factor’, n1of the linear two-port active network. A lower limit of 10, proposed earlier for the ‘invariant stability factor’, s, is shown as equivalent to a lower limit of 4 for Sd. The role of the performance factor in the maximum power gains of mismatched and optimum unilateralized single active stages is emphasized. Finally, variations in thetotal port immittance due to changes in terminating immittance at the opposite port are expressed in terms of the performance factor