Performances of standardised XPSP in the U band of JKC system for the Stetson validating sample. The meaning of the symbols and the arrangement of the plot are the same as in Fig. E.1, except for the y-axes scale, which is much more expanded here. The 29176 stars in the Stetson validating sample having their XP spectra released in Gaia DR3, G < 17.65, and valid U_Stet and U_STD magnitudes are represented as grey dots, while those shown as a viridis density maps are the 9157 that also have flux_U/flux_error_U> 30. P₅₀, P₁₆, and P₈₄ lines refer to the latter subsample.