Evolution of the normalised frequencies of non-radial ℓ = 1 modes, with radial order n = 11, for evolutionary tracks of a stellar grid (the details of which are given in Section 3) with masses between 1.23 and 1.27 M_⊙, as a function of the physical age τ (top) and the central density ρ_c (bottom). The points connected by a dashed line in the top panel indicate models with an age of 4.18 Gyr. The bottom panel displays a subplot that zooms on a particular avoided crossing for the mass M = 1.24 M_⊙.