3D velocity components of NGC 104 with respect to the mean cluster velocity, as a function of the position angle θi . The combined sample of RGB, AGB, HB, and MSTO stars in each velocity catalogue are shown as black points with errorbars. Top panel: the radial component of the proper motion, with the mean value shown in green. Middle panel: the same as the top panel, but for the tangential component of the proper motion. Bottom panel: the LOS velocity as a function of θi, with the sinusoidal fit to the distribution shown in green and the position angle of the rotation axis θ0 shown as a white star with errorbars.