Comparison of our results with those of Barnes et al. (2016). Panel a shows a CPD as in Fig. 9 and overplotted in red are the measurements by Barnes et al. (2016). The gray lines, solid and dashed, are our indication of the cluster and half-period sequences, respectively. Panel b shows a CMD of the same stars and the inset (panel c) the proper motions centered on M 67. Gray dots in panels b and c are members without period determinations.