Against the background of the working hypothesis of the 1-parametric Siregnost FD 5 forced oscillation technique-phase angle psi may be invariant in a clinical reference population-the hypothetical straight Ros-P line is in good agreement with the crowd of extremely nonlinear Rre-P-lines only within narrow limits. Neglecting phase angle measurements it might be useful to insert a known linear resistor into the airway to determine the pertaining Rre-P relation. In spite of selective tuning to the oscillation frequency of 10 Hz there is full sensitivity to stationary flow; alinear stationary flow characteristics of resistors can be readily determined by forced oscillation. There is a marked improvement in the P-psi/Rre-phi-evaluating system with respect both to the symmetry of phase angle and unequivocality of pressure when the reference phase angle alpha is shifted from 81 degrees to 0 degrees. Using digital data acquisition and processing, a flexible evaluation technique with monitor-oriented test management, automatical calculation of secondary values and multidimensional presentation of results on a graphical display is provided, which has proved its worth in experimental and clinical-physiological studies.