  In view of the progress achieved in the field of the ac quantum Hall effect,
the Working Group of the Comite Consultatif d'Electricite et Magnetisme (CCEM)
on the AC Quantum Hall Effect asked the authors of this paper to write a
compendium which integrates their experiences with ac measurements of the
quantum Hall resistance. In addition to the important early work performed at
the Bureau International des Poids et Mesures and the National Physical
Laboratory, UK, further experience has been gained during a collaboration of
the authors' institutes NRC, METAS, and PTB, and excellent agreement between
the results of different national metrology institutes has been achieved. This
compendium summarizes the present state of the authors' knowledge and reviews
the experiences, tests and precautions that the authors have employed to
achieve accurate measurements of the ac quantum Hall effect. This work shows
how the ac quantum Hall effect can be reliably used as a quantum standard of ac
resistance having a relative uncertainty of a few parts in 10^8.
