Bruce, Problem is that when we do the fit in derivative and, save the results, something other than first derivative is written to the file. Have you ever looked at the saved/written file of a first derivative fit? Thanks, Ganga -------------------- Ganga M. Hettiarachchi, Ph.D. Assistant Professor of Soil and Environmental Chemistry Department of Agronomy 2107 Throckmorton Plant Sciences Center Kansas State University Manhattan, KS 66506 USA 785-532-7209 (office) 785-532-6094 (FAX)