Examination of the Combined Catalogues of IERS

Based on the relationship between the coordinates of sources in the combined catalogues and individual ones, extensive comparisons are performed in this paper. It is shown that source coordinates tabulated in each combined catalogues of IERS from 1988 to 1991 are not given in a compatible coordinate system. Deviations of several milliarcseconds are detectable in the coordinates of some sources. The problem of inhomogeneous coordinates also makes unexpected effect on the maintenance of the orientation of the IERS celestial frames, which is just on a level of mathematical meaning withont definite physical one.