Dear all, phenix.xtriage estimates a twin fraction of between 24 and 30% but then when I start the refinement I get 47-49%. In CNS if I fix the twin fraction in a series of refinements the Rfactors jump from 44% (twin fraction 0) to 37% (from 25% to 49%, only marginal improvement upon going from alpha=25% to 49%). Questions: 1. Is the refinement of alpha dependent on the model? 2. I am tempted to work with the 30% that xtriage estimates but do not know how: is there a way to fix alpha? Thanks Pietro -- Sent from my Desktop Pietro Roversi EP Abraham Fellow in Biochemistry - Lincoln College - Oxford Sir William Dunn School of Pathology, Oxford University South Parks Road, Oxford OX1 3RE, England UK Tel. 0044-1865-275385