The astrometric accuracy of “Carte du Ciel" plates and proper motions in the field of the open cluster NGC 1647M. Geffert, P. Bonnefond, G. Maintz and J. GuibertAstron. Astrophys. Suppl. Ser., 118 2 (1996) 277-282DOI: https://doi.org/10.1051/aas:1996196