Top panel: phase shift of the central radial mode for a sequence of 1.0, 1.5, 2.0, and 2.5 M_⊙ ascending RGB models. Descending RGB and core He-burning models are shown only for the 2.5 M_⊙ track. Bottom left panel: the models from the top panel shown in a theoretical HR-diagram with the models shown in the bottom right panel indicated with black symbols. Bottom right panel: normalised échelle diagram showing the radial modes of 1.0 (red diamonds) and 2.5 M_⊙ (blue circles) RGB models and 2.5 M_⊙ (grey squares) RC models. The blue and grey lines indicate a linear fit to the RGB and RC mode sequences, respectively. The grey and red symbols are vertically shifted for better visibility. Colours are only given in the online version.