Hi Elaine and ChimeraX Team My query relates to measuring rotation between two subunits from homologous models in ChimeraX. Here, I have first aligned the two models on one of sub-domains of these multi-domain complex. Then, without moving the models, the plan is to calculate the rotation in another domain, between the 2 models, apart from measuring the translational shift. So, * Align Chain /L,M (model #1, PDB:6g2j ) and Chains /5,4 (model #2, PDB:6rfr). * Calculate rotation of Chain /F (model #1, PDB:6g2j) and Chain /B (model #2, PDB:6rfr). I am using the following commands: -- open 6g2j; open 6rfr; -- match #1/L,N to #2/5,4 pair ss; -- measure rotation #1/F toModel #2/B coordinateSystem #1/F showAxis true showSlabs true; The log report is: Position of 6g2j #1 relative to 6rfr #2 in 6g2j #1 coordinate system: Matrix rotation and translation 0.80441124 0.40360431 -0.43591986 67.76279700 0.18783349 0.52334489 0.83116106 -121.82969657 0.56359661 -0.75047565 0.34517410 202.31442783 Axis -0.83978100 -0.53070022 -0.11456502 Axis point 0.00000000 87.13355460 206.39866592 Rotation angle (degrees) 70.33834463 Shift along axis -15.42901832 Thus, ChimeraX is calculating a rotation of ¬70 degrees, which is clearly the case. The visual inspection suggests, that the rotation should be no more than ~15-20 degrees. I am not sure where I am going wrong. Could you please help? Thanks Yaikhomba