Dependences of relative errors of PSD (a, c) and energy reflection coefficient (b, d) of wave 1 on the main layer (silver) thickness when the investigated multilayer is replaced by one main layer on the same substrate (d_1,3,4 = 0) for various wavelengths of the incident TM polarized wave. For all the graphs, thicknesses d_1,3 are given in the figures, d₄ = 5 nm, ψ = π/6, ϵ_β = − 0.2 + 0.1i, μ_β = 1, the spacer layers material is SiO₂ (ϵ_1,3 = 2.13 + 2.92 × 10⁻⁷ i, µ_1,3 = 1 [45,46]), and the additional layer parameters are: ϵ₄ = 3 +0.5i, µ₄ = 1.5 + 0.2i.