Echelle diagram of Kepler 91 comparing observed oscillation frequencies (listed in Table A.1) represented as squared points and theoretical oscillation frequencies represented as circle points. The whole modelled oscillation spectrum for the ℓ = 1 modes is included with shaded points. The difference between observed and modelled data is quantified, in the legend, as a χ² for each spherical order ℓ. Finally, the error bars on the observed frequencies are included in the data points and not clearly distinguishable here.