Institute of Astronomy, Moscow, Russia
The systematic accuracy of the catalogues representing the principal independent normal systems made in the 19th and 20th century centred on different epochs, NFK, FK3, FK4, FK5, N2, GC, N30, are investigated by use of the proper motions of the N70 system, compiled on the basis of modern catalogues, on one hand, and some of the abovementioned fundamental catalogues, on the other hand. The method of the N70 system construction will be presented, its internal and external accuracy will be discussed. The systematic differences between N70 and the 19th - 20th century normal systems will be tabulated and presented. These will form the basis of external accuracy estimation of the normal systems which will be compared with the internal errors of the systems given for some of them. Possibility to use these normal systems of positions for checking of the HIPPARCOS system at distant time intervals will be estimated as a result. The possible combination of the most accurate ground-based and space catalogues to improve the system of proper motions will be discussed in details.