Hi List, I have tried a variety of different things to get this fit to work. It seems pretty decent now, although, for my two MS paths (4,5) I had to force the sO^2's to be positive. In the process one of them is now zero. My parameter 'amp' wants to be 0.5 so I had to set it to 0.7 because I know that it shouldn't be as low as 1/2. Changing the k-weight doesn't seem to help. Here's my Data: Thanks, Dan Project title : Fitting merge 10_15_04.chi ============================================================ Independent points = 28.581054688 Number of variables = 13.000000000 Chi-square = 5995.284754934 Reduced Chi-square = 384.780419245 R-factor = 0.043668737 Measurement uncertainty (k) = 0.000187262 Measurement uncertainty (R) = 0.006509968 Number of data sets = 1.000000000 Guess parameters +/- uncertainties (initial guess): e0 = 0.8645560 +/- 1.2283680 (guessed as 0.864556 (1.228344)) ss = 0.0041070 +/- 0.0005190 (guessed as 0.004107 (0.000519)) ss2 = 0.0043590 +/- 0.0005200 (guessed as 0.004359 (0.000520)) ss3 = 0.0217810 +/- 0.0333390 (guessed as 0.021781 (0.033341)) ss4 = 0.0000000 +/- 0.0509500 (guessed as 0.000000 (0.050951)) ss5 = 0.0000360 +/- 0.0063810 (guessed as 0.000036 (0.006382)) ss6 = 0.0028730 +/- 0.0071340 (guessed as 0.002873 (0.007133)) alpha = -0.0012530 +/- 0.0031940 (guessed as -0.001253 (0.003193)) alpha2 = 0.0075160 +/- 0.0022250 (guessed as 0.007516 (0.002225)) alpha3 = -0.0171580 +/- 0.0323200 (guessed as -0.017158 (0.032321)) alpha4 = -0.0165410 +/- 0.1054840 (guessed as -0.016541 (0.105487)) alpha5 = -0.0181860 +/- 0.0187940 (guessed as -0.018186 (0.018795)) alpha6 = 0.0227330 +/- 0.0147690 (guessed as 0.022733 (0.014767)) Def parameters: delr_1 = -0.0057180 delr_2 = 0.0342980 delr_3 = -0.0782970 delr_4 = -0.0754820 delr_5 = -0.0829880 delr_6 = 0.1037370 Set parameters: amp1 = .7 Correlations between variables: ss3 and alpha4 --> 0.8462 e0 and alpha --> 0.8335 ss4 and alpha3 --> -0.6693 e0 and alpha2 --> 0.6159 ss and ss2 --> 0.6114 alpha5 and alpha6 --> -0.5959 alpha4 and alpha5 --> -0.5821 ss4 and ss5 --> -0.5505 ss3 and alpha5 --> -0.5246 alpha and alpha2 --> 0.5146 ss5 and ss6 --> -0.4931 ss2 and alpha5 --> 0.4681 ss5 and alpha3 --> 0.3885 ss6 and alpha6 --> 0.3700 alpha2 and alpha5 --> 0.3208 ss2 and alpha4 --> -0.2992 ss4 and alpha5 --> 0.2955 ss3 and ss4 --> 0.2923 ss5 and alpha2 --> -0.2842 e0 and alpha4 --> -0.2781 ss2 and ss3 --> -0.2677 alpha3 and alpha5 --> -0.2523 All other correlations are below 0.25