Density distribution of residuals as a function of wavelength for VMP stars. Top panel shows the density distribution of the residuals of VMP stars with 1.0 < G_BP − G_RP < 1.2 and 13 < G < 15. Compared to the relatively more metal-rich sample in Figure 1, their wiggles have a smaller amplitude with Max (|P₅₀|) < 0.08. The bottom panel shows the difference of P₅₀ between these two samples. The main difference is in the blue band of λ < 6500 Å, while the wiggles in the red band is little affected by the change of metallicity.