PM “systematics” in radial (blue triangles) and transverse (red squares) directions, as a function of distance to the cluster centre. The cyan line is a fit to the variation of the mean radial component of the PMs as a function of distance, while the grey line is the expected trend resulting from perspective contraction or expansion. From left to right: NGC 6656 shows a strong rotation signal as well as perspective expansion; NGC 3201 shows no rotation but very strong perspective contraction; and NGC 6397 shows halo expansion associated with core collapse, clearly different from the signal expected from the small perspective contraction. The vertical line indicates the tidal radius of the cluster reported in Harris10.