Comparison of rotation curves of the different samples. We show the mean azimuthal velocity for the open clusters (dark blue) and Cepheids (yellow) as a function of galactocentric radius (calculated as explained in the text), compared to the profiles of the OB (light blue) and RGB stars (turquoise). Coloured points show the single sources for the Cepheids (black dots) and OCs (red points).