Diagnostic diagrams of the rotation signal detected in M75, within 7″ from the cluster center. Left panel: difference between the mean RV on each side of an axis passing through the center as a function of the PA of the axis itself. The red line is the sine function that best fits the observed pattern, while the red shaded region marks the confidence level at 3σ. Central panel: distribution of the RVs referred to V_sys (V_r), as a function of the projected distances from the rotation axis (XR) in arcseconds. The value of PA₀ is labeled. The dashed red line is the least square fit to the data, and the red shaded area represents the 1σ uncertainty of the linear fit. Right panel: cumulative V_r distributions for the stars with XR < 0 (solid line) and for those with XR > 0 (dotted line). The KS probability that the two subsamples are extracted from the same parent distribution is labeled.