Period spacing in the co-rotating frame as a function of the spin parameter for the modes of the series (ℓ = 1, m = −1) at different rotation rates using the 1z model. The period spacing is normalised by the buoyancy radius Π₀. The pink line shows the traditional approximation of rotation. The square dots indicate the modes that are within the range of typically observed radial orders 30 < n < 70. The dashed line corresponds to the frequency of the resonant inertial mode ℓ_i = 3, m = −1 calculated analytically with the uniform density model.