1. Renishaw Transducer Systems Limited, Old Town, Wotton Under Edge, Gloucestershire, GL12 7DG, U.K. (K.P.J.W., G.D.P.); Department of Physics, University of Leeds, Leeds, U.K. (D.N.B.); and DSM Research, P.O. Box 18, 6160MD Geleen, The Netherlands (B.J.K.)