Velocity dispersion as a function of Na abundance for NGC 104, NGC 2808, NGC 288, NGC 1851, NGC 1904, NGC 3201, NGC 4590, and NGC 5904. Larger filled squares indicate cases where one star has been clipped from the sample because of an RV value more than 3 − σ from the mean. Only estimates obtained from  ≥ 10 stars (after clipping) are plotted. The vertical scale is different for NGC 104 and NGC 2808, to accommodate for the larger dispersion of these clusters.