The decomposition of the projection factor. The filled and open diamonds correspond to the Milky Way and LMC models of δ Cep. For a given model, the lower (resp. higher) values are the amplitudes of the radial (resp. pulsation) velocity curves for each spectral line considered. The red and blue arrows indicate the decomposition of the projection factor for the MW and LMC respectively:  ↑  (p₀),  ←  (f_grad),  ↓  (f_og) and  ↖  (p = p₀f_gradf_og). For detailed explanations, refer to Nardetto et al. (2007).