Comparison between synthetic photometry computed on external high-resolution spectra and on ECS in the HIPPARCOSH_p and TychoB_T, V_T photometric system. SPSSs are represented as open red circles, PVLs as blue crosses, and NGSLs as open green triangles. The difference between the two sets of magnitudes is shown as a function of G magnitude (left) and colour index G_BP − G_RP (right). Two horizontal lines at ±0.02 are shown for reference.