Hi everyone, I have a P31 twin crystal, resolution 2.0, and with twin fraction 0.451. I use phenix.refine to refine the structure and with freeR set to 8%. % phenix.refine data.sca model.pdb twin_law="h,-h-k,-l" xray_data.r_free_flags.generate=True xray_data.r_free_flags.fraction=0.08 Result: Final: r_work = 0.1793 r_free = 0.2258 bonds = 0.011 angles = 1.557 REMARK 3 FREE R VALUE : 0.2258 REMARK 3 FREE R VALUE TEST SET SIZE (%) : 3.67 REMARK 3 FREE R VALUE TEST SET COUNT : 2013 After the refinement, it seems like my freeR set size reduced by half (3.67%). Is it due to the twin effect, or something is wrong with my refinement? And if I use ccp4 program "scalpeak2mtz " to convert the .sca to .mtz and with freeR fraction set to 8%. Then refine it with phenix. % phenix.refine data.mtz model.pdb twin_law="h,-h-k,-l" Final: r_work = 0.1669 r_free = 0.1970 bonds = 0.010 angles = 1.406 REMARK 3 FREE R VALUE : 0.2022 REMARK 3 FREE R VALUE TEST SET SIZE (%) : 7.80 REMARK 3 FREE R VALUE TEST SET COUNT : 4326 It turns out, my test set is still 8%, and R/Rfree looks even better than the first one. So I am wondering which one is the correct one and why? Thanks! Lauren