Hi, Well, I guess one shouldn't change versions of refmac in the middle of a structure refinement. What are the major differences between . 0034 and .0066 ? I noted that form factors for the Se atom have changed dramatically even though I'm using the same " anom formfactor SE -8.13 5.05 " command. Is this because the program is now using the wavelength on the .MTZ file ? with .0034: SE 8.8706 2.4098 5.8196 0.2726 3.9731 15.2372 4.3543 43.8163 2.8409 with .0066: SE 8.8706 2.4098 5.8196 0.2726 3.9731 15.2372 4.3543 43.8163 2.8409 The other major difference is that explicit weight that I was using = 0.25 is weighting the geometry much more in .0066 compared with . 0034. Also the refinement is not as well behaved as it was in 0.0034. What has really changed? Mark _________________________________ Mark A. Saper, Ph.D. Associate Professor, Biophysics and Department of Biological Chemistry University of Michigan 3040 Chemistry Building 930 N University Ave Ann Arbor MI 48109-1055 [log in to unmask] phone (734) 764-3353 fax (734) 764-3323 Research summary