Properties of the IAU commission 30 RV standard stars. Top: distribution in the colour-magnitude plane. Stars brighter than V = 6 (small open circles) are too bright for RVS standards, and will therefore not be kept for our list. Filled circles indicate IAU standards fainter than V = 6, suitable for RVS. Bottom: sky distribution of the IAU standards (symbols as for the top panel). A large fraction of the usable standards is located in a strip around δ =  + 30°, with a clear lack of standards in the southern hemisphere.