the use of hybrid parameters is well suited to transistor circuits, because these parameters are among the most convenient to measure experimentally for a transistor. The difficulty in measuring, say, the open-circuit impedance parameters arises when a parameter such as Z11 must be measured. A known sinusoidal current is easily supplied at the input terminals, but because of the exceedingly high output impedance of the transistor circuit, it is difficulty to open-circuit the output terminals and yet supply the necessary dc biasing voltages and measure the sinusoidal output voltage.