Evolution of the period of the ℓ = 1 gravity modes with decreasing central hydrogen content. The theoretical frequencies were calculated with GYRE in our region of interest along the MESA evolutionary track which holds the best fitting model (ℳ = 3.20 ℳ_⊙, Z = 0.020, f_ov = 0.000). The colour of each model (a set of GYRE frequencies along a vertical line) represents the logarithm of the corresponding χ² value at the given X_c (using the same colours as Fig. 10). For better visibility, this colour sequence is repeated on the top of the figure. The observed modes are plotted using larger red circles at the position of the best fitting model at X_c = 0.6932 (the error bars on the observed values are smaller than the size of the symbols).