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Hi -- I have a twinned data set -- approximate twinning fraction of 0.4. I decided to try to try twinned refinement using phenix.refine in what would seem to be the appropriate manner -- from the "All Parameters" menu, I select twinning, hit "Run Xtriage now" on my mtz file, it gives me the input to the "Twin Law", I keep the rest of the values the same (gave no Anisotropy correction), hit OK, then run 3 cycles of refinement. The only thing is that the Rwork/Rfree values are really very good, almost too good to be true -- for my 1.7 A refinement, I have values of 12.4 and 14.8%, respectively for Rwork and Rfree. Is there anything that I may be doing wrong yielding R values which are artifically too low? Thanks for your help Alex -- Dr. Alex Singer C.H. Best Institute 112 College St. Room 70 University of Toronto Toronto, Canada, M5G 1L6 416-978-4033