Location of RGB stars with nonconstant ΔΠ₁ in the (Δν, ΔΠ₁) plane. Black star symbols correspond to the values of ΔΠ₁ that produce the best vertical alignment of modes in the stretched period échelle diagram (Sect. 2). Colored star symbols correspond to the corrected values of ΔΠ₁ obtained by taking into account the magnetic perturbation to the mode frequencies (Sect. 4). Other RGB stars from Vrard et al. (2016) are shown as gray circles (for clarity, stars flagged by the authors as potential aliases were omitted).