The rotational splitting normalized to its maximum value as a function of ζ (black dots) for model M1 (top) and model M2 (bottom). The red crosses represent the approximation δν/δν_max = ζ as a function of ζ. The blue crosses represent the approximation δν/δν_max = ζ(1 − 2ℛ) + 2ℛ as a function of ζ with R = 0.1785 and using numerical values of ζ.