I wanted to add a coupe more comments on Stafano's questions regarding k-weighting in Athena and Artemis. Regarding k-weights in Athena: Athena's default for the k-weight using background removal is 1. I chose that pretty much for the reason that Scott gave. Ifeffit's default is 0, so this is a situation where Athena and Ifeffit have different default behavior. As for the insensitivity of your data to this value, I would say that it is situational. Sometimes, the k-weight can have a dramatic influence on the background removal. Stability of the background removal and its impact on subsequent analysis has been a frequent topic of discussion in this forum. k-weight, then, is yet another parameter that can impact the stability of your spline. Rgearding k-weights in Artemis: Scott and Matt covered the "why" of k-weights. How k-weights are actually used by Artemis when fitting and plotting is a bit complicated. See section 5.8.4 of the (incomplete) artemis document for a detailed explanation of how k-weighting is used in Artemis. http://leonardo.phys.washington.edu/~ravel/software/exafs/doc/artemis.pdf B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 405 Naval Research Laboratory phone: (1) 202 767 2268 Washington DC 20375, USA fax: (1) 202 767 4642 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/