Mass-radius relationships at different ages in the fully to partly convective transition region (solid line). We note that the mass grid uses a spacing of 0.01 M_⊙. To highlight changes in the slope, the dashed curve is a straight line connecting values of the radius between 0.3 M_⊙ and 0.4 M_⊙. The dash-dotted (red) curves correspond to the test case where ³He is forced to reach equilibrium (see Sect. 2.2).