In Photographic Astrometry the absolute proper motions of stars are determined relative to galaxies by the direct (I) or indirect (II) methods. In the direct method the plate constants are determined directly from galaxies, used as the reference stars with a Zero proper motion. In the indirect method the proper motions are first found relative to the totality of reference stars Sr (r=1, 2,… r0), then the obtained relative proper motions are reduced to absolute values by means of galaxies Gg (g = 1,2,… g0), the correction, identical for all the stars, being derived by formula (I).