Graphs of Cu (and other elements) coefficients can be found at http://www1.usa1.com/~aic/2121.html Tables of coefficients can be prepared by PHOTCOEF, see http://www1.usa1.com/~aic/21.html All these coefficients are based on NBS data (now National Institute of Standards and Technology) Paul Kehler AIC SOFTWARE P.O. Box 544 Grafton, MA 01519 Tel: 508-839-6779 Fax: 508-839-4853 photcoef@aol.com