Petersen diagrams showing the frequency ratios for various pairs of radial modes as a function of the fundamental frequency (left panels) and the first-overtone frequency (right panels). The individual panels display the ratios of: (a) p₁ and p₂, (b) p₂ and p₃, (c) p₁ and p₃, and (d) p₂ and p₄. The effect of varying individual parameters is illustrated. The observed values for the selected frequency pairs are marked with asterisks.