Hi Scott, here I copy a part of the report: Independent points = 6.222656250 Number of variables = 4.000000000 Chi-square = 247.145092496 Reduced Chi-square = 111.193574128 R-factor = 0.017422216 Guess parameters +/- uncertainties (initial guess): amp = 6.7815290 +/- 1.4687660 (1.0000) enot = 2.2173620 +/- 2.1499920 (0.0000) delr = 0.0514640 +/- 0.0163900 (0.0000) ss = 0.0074020 +/- 0.0025220 (0.0030) I see that the R-factor is pretty good, 1.74%, amp is high cause is correlated with the coordination number and always have big errors., delr has the error of the total distance, so it is ok, but ss and enot have a a really big error, is this normal? Thanks, euG