Copyright © The Numerical Algorithms Group 1996. Published by The Numerical Algorithms Group Limited. NAG and the NAG logo are registered trademarks of The Numerical Algorithms Group Limited. IRIS Explorer is a trademark of Silicon Graphics, Inc. All other trademarks are acknowledged. Thunderstorm data provided courtesy of Dr Robert Wilhelmson, NCSA, University of Illinois. Rotating cylinder and cavity flow data provided courtesy of CJ Were, Dept of Mechanical Engineering, University of Auckland. PHOENICS data provided courtesy of CHAM Ltd. ROSAT data provided courtesy of Dr Wolfgang Brinkmann, Max Planck Gesellschaft, Garching.