Dear all After reading the informative posts in mailing list, I started to deal with my first twinning dataset. The space group is P3. Xtriage found 3 twin laws. R vs R statistics indicated perfect twinning for two twin laws and one is twin with RPS. I realize that twin-related reflections should be in the same work or free group. Could phenix handle the Rfree flag correctly for me when there are more than one twin fraction identified? By applying one twin law, the Rfree dropped from 37% to 28% using phenix. When I use Refmac, the twin fractions are refined and the Rfree is down to 26%. I copied the Rfree flag from phenix to the ccp4 in this case. When I let ccp4 generate Rfree flag automatically, the Rfree is refined to 26% too. Should I label the Rfree at a higher space group? Thanks for your advice Best, Zheng (Joe) Zhou