There is an internal catalogue containing the names, positions and guide star references for up to 500 objects. The user deals with 3 special entries: the EDIT source is the catalogue entry whose parameters (RA, Dec, equinox, proper motions, guide object) are presently being modified; the CURRENT source is the object being observed and the NEXT source is the object that will be observed when the TELESCOPE-DOME SOURCE button is pressed or the GO command is typed (at which point it also becomes the CURRENT source). Modifications to the CURRENT source's parameters do not affect the operation of the telescope directly. This is only altered when a button is pressed or GO is typed, in which case the parameters of the NEXT source are always picked up. When a new catalogue entry is defined using the SOURCE command, it automatically becomes the EDIT source.