Dear BB, Sorry for the obvious question, but I couldn't find a description of the syntax for the FreeR flag function in phenix.refine. Is there a paragraph on the phenix web site that explains what I should put in these fields: r_free_flags { file_name = "S19_sigmaa1.mtz" label = "FreeR_flag" test_flag_value = 0 --> don't know what this means? disable_suitability_test = False --> implications of this? I was running refinement from an mtz file from sigmaa in ccp4 with an appropriate FreeR flag designated in the MTZ file. phenix.refine worked fine and seemed to exclude the test reflections, but I wanted to know what these commands do. Cheers, Simon.