Top: axisymmetric potential Φ₀(R) from Eq. (3) (units are M_⊙, kpc, and Myr). Positions of the Sun and the ILR are indicated by the vertical lines at 8 kpc and 2.13 kpc, respectively. Bottom: equatorial non-axisymmetric components of the perturbation potential: the spiral arms perturbation, Φ_sp(R, φ) (red curve), and the bar perturbation, Φ_bar(R, φ) (blue curve). The calculations were done in direction of the bar’s major axis, with the phase φ = 67.°5, and with the parameters taken from Table 1. We note that all components are plotted with positive sign, in logarithmic scale; in this case, they are referred to as force functions.