Diagnostic diagram for Hβ. Every parameter was calculated by using two Gaussian lines with the same FWHM. Shown from top to the bottom, plotted vs. the peak-to-peak separation, are the semi-amplitude velocity K₁, the ratio of K₁ to its associated error, the systemic velocity γ, and the corresponding phase shift. The vertical red line represents the peak-to-peak separation (a = 3800 km s⁻¹) above which the measurements begin to be contaminated by noise in the continuum, as inferred from the plot in the second panel.