Period spacing as a function of the period for model 1z with different value of the uniform rotation frequency, ranging from 7 μHz to 23 μHz, by increment of 2 μHz, for zonal dipolar modes. Both the period spacings and the periods are shown in the inertial frame of reference. The filled circles are obtained with non-perturbative calculations, while the grey curves are obtained with the traditional approximation of rotation. The vertical lines give the location of the periods of pure inertial modes associated with different rotation rates (only for ν_rot = 13 to 23 μHz), computed for an incompressible inviscid spherical box as described in Sect. 2.2.