While experimenting with twin refinement for a crystal in P321 that approximates P622 to varying extents, I noticed: | twin fraction: 0.59 twin operator: -h,-k,l | A bug, perhaps ? This twin fraction would seem to be unlikely, since twin fractions > 0.5 have no meaning. Since this data does not scale well in p622 compared to some more heavily-twinned datasets on this xtal form I think the twin fraction is certainly less than 0.5. Xtriage estimates: Statistics depending on twin laws ----------------------------------------------------------------- | Operator | type | R obs. | Britton alpha | H alpha | ML alpha | ----------------------------------------------------------------- | -h,-k,l | M | 0.150 | 0.343 | 0.347 | 0.283 | ----------------------------------------------------------------- Unless of course phenix.refine is reporting 2*alpha. Phenix v1.4-3 Intel Mac OSX 10.5.6 This particular run with: phenix.refine model-08.pdb pz7e_truncate-unique.mtz refinement.main.ncs=true strategy=individual_sites+group_adp --overwrite xray_data.r_free_flags.generate=True twin_law="-h,-k,l" This is a very early non-finessed model. Phil Jeffrey Princeton