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