Dear All, I am trying to fit the first shell FT of bulk YbVO4 (measured in dispersive EXAFS) with the reference YbVO4. The resultant SS2 value for the first shell is found to be low for wide k-range selection, whereas approaching negative for the relatively short k-range window. While approaching negative value (of ss2), i have tried to constraint the ss2 value using expression abs(ss). In that case, ss2 value is found to take value 0. Please help me to figure out the problem. Further i have found a small bug in the fit history window. After each fit, earlier data set in the log file of fit history is found to overwritten with the latest fitting parameters (like k range, dk, etc..). Here in my log file window, all fit data set contain the same data set value as like the last fit (fit9). Regards, Raj