Alan, I also should have mentioned that: Statistical Distributions by Evans, Hastings & Peacock, Wiley ISBN 0-471-55951-2 is a good handy reference covering heaps of distributions. Glenn Crouch mailto:[log in to unmask] ICQ:36017076 ESB Consultancy, http://www.esbconsult.com.au Home of ESBPCS, ESBStats, ESBPDF Analysis & ESBCalc Kalgoorlie-Boulder, Western Australia (TeamND, TeamOE, Addict Support, eLists.org Management)