Dear phenixbb, I am using the "reflection file editor" in phenix 1.8.1-1168 to generate my test set (with the GUI). I have NCS so I ticked the box "assign test set in thin resolution shells". I also have twinning, and want to have my Rfree not biased by twin related reflections. I guess the option "use lattice symmetry to generate test set" is the one I should use for this purpose? I couldn't find much information online about this option. No log file has been generated so I can't check what happened. I am supposing xtriage is ran in the background and if a twin law is found, then used to generate the test set. My output from xtriage is: Statistics depending on twin laws ----------------------------------------------------------------- | Operator | type | R obs. | Britton alpha | H alpha | ML alpha | ----------------------------------------------------------------- | -k,-h,-l |PM| 0.249| 0.272| 0.246| 0.200| ----------------------------------------------------------------- And indeed if I check in mtzdmp the output mtz, reflections in the test set are related by (-k, -h, -l); disclaimer: I only checked in the plane (h,k,0). I would like to be sure my Rfree is generated correctly. Alternatively, what would happen when multiple twin laws are available? Is the most probale used? Is it possible to specify the editor which law to use? Thank you for your help. Vincent -- Vincent Chaptal, PhD Institut de Biologie et Chimie des Protéines Drug-resistance modulation and mechanism Laboratory 7 passage du Vercors 69007 LYON FRANCE +33 4 37 65 29 01 http://www.ibcp.fr