Dear all, Recently I have got a data set that diffracts to 1.7 angstrom. Images look good. During data processing I did not find anything that looks strange. However, when I was doing Phaser-MR, I got a warning: “ Intensity moments suggest significant twinning (>5%). Tests based on possible twin laws will be more definitive.” What does this mean? A twinning data set? I still found a solution and refined the model step by step, using the data (20-1.7 angstrom). It seems that the final model and map are acceptable. But R-factors are 0.24/0.28, very high. Does the twin cause the high R-factors? Is there a solution to detwin? Or are the R-factors acceptable for a twinning data set? Any suggestions are appreciated and thanks in advance! Best, Shun