Selection of cluster member stars using the example of NGC 1856. (a) The m_F814W vs m_F438W–m_F814W CMD of well-measured stars in the field of the cluster for which PMs have been determined (b) 1D relative PMs as a function of the m_F814W magnitude. The blue line (drawn by hand) follows our selection of likely cluster members (black dots) based on their motions. The dependence on the magnitude is to account for the varying PM uncertainties as a function of magnitude. (c) CMD of PM-selected cluster members. (d) CMD of PM-selected cluster stars, including only stars within one effective radius from the cluster centre.