Overall Philosophy of the Echelle Spectrographs for the Anglo-Australian Telescope and William Herschel Telescope

Two large echelle spectrographs are under construction which will provide essentially identical spectra at observatories in the northern and southern hemispheres. Observers will see the same software for instrument control and data reduction at both observatories, and on the UK STARLINK network. This paper considers how such an instrument fits within the overall system, and draws conclusions which are relevant to other instruments in the future.