Transmission properties of a telecommunications transmission line may be estimated with improved accuracy by numerical solution for Γ of Zin·jω^C=Γcoth(Γ). At least one curve is adapted to Γ solutions already obtained and a starting point for numerical solution is selected in dependence of the at least one curve and in dependence of an already obtained solution close in frequency. In a first frequency range, starting points for numerical solution may be calculated from a biquadratic equation. In a second frequency range, a line in the complex plane may be adapted to solutions already obtained and new starting points selected in dependence of the line and in dependence of the previous solution. In a third frequency range, two lines in the frequency plane may be adapted to solutions already obtained and new starting points selected in dependence of the lines.