The principles of the conception and design of control-rooms of nuclear power plants used in Germany are laid down in KTA 3904 more detailed requirements internationally in DIN EN 60964 (VDE 0491-5-1):2010-08. The standard DIN EN 61839 (VDE 0491-5) deals with the aspects of the functional analysis and the assignment of functions in detail and, as such, it can be recongnized as a supplement to KTA 3904 and to DIN EN 60964 (VDE 0491-5-1). It is, in principle, also applicable to backfits and modernization of existing control-rooms.