Measured RVs of the stars with respect to their distances from cluster centres over the r_t of each cluster. Red dots are the stars having RV measurements in the literature. The grey line is used for the mean RVs of the clusters, while the black lines represent the RV dispersion. Red lines in the M 54 panel are the limits on the RVs adopted by Bellazzini et al. (2008). The closest star to NGC 4147 has a larger RV error of ∼80 km s⁻¹, extending beyond the limits of the plot.