Acquisition and Guiding (A&G) units are available at the Prime, Cassegrain and
UES Nasmyth foci of the WHT. Autoguiding is also possible at the GHRIL
focus (with derotation optics) using a pellicle beamsplitter to feed
a television camera. Guide stars for the autoguiders can normally be
found with the Guide Star Server (GSS) system, which uses the
HST's Guide Star Catalogue; this is described in section