Relative period spacings ΔP/ ΔΠ₁ and relative rotational splittings ζ for a synthetic RGB mixed-mode spectrum. The red line shows the asymptotic ζ function; the blue crosses represent the period spacings derived from the asymptotic expansion of mixed modes and scaled to ΔΠ₁. The dashed line shows the minimum values ζ_min reached by pressure-dominated mixed modes; the dotted line shows the maximum values ζ_max reached by gravity-dominated mixed modes.