Predicted and observed period spacings as a function of ν_max. Isochrone details are in the text and in legend of Figs. 1 and 7. For clarity, not all isochrones are shown. For reference, the isochrone RGB phase begins on the left-hand side and reaches the RGB tip on the lower right before returning left through the contracting HeCB phase, then taking another shift to the right at the beginning of the stable HeCB phase. This happens at the point (93, 208) for the dark green full-drawn thick 0.43 Gyr isochrone. The black arrows mark the observed period spacings which are extreme lower limits of their asymptotic counterparts. The red dashed line connects the observed and asymptotic period spacing for the one star that has both measurements. The red circles are the observed period spacings shifted by the amount of the red dashed line and represent an approximation of the asymptotic period spacings, assuming that the difference between the observed and asymptotic period spacing is similar for all five stars.