Hi All I am interested to measure the angle between chain A and chain B of heterodimer, and both sequence identity is around 14%. I can measure the angle by selecting 3 atoms on chain A and chain B but this is bias because, if I change the residues then the angle will be different. I can also measure by structure measurement options and defining the axes and all the create axes for all the helices in the chain A and chain B and measure the angle between two helices on chain A and chain B. I am not sure if its a right way to claim the angle between chain A and chain B in one PDB file. I also try to use the "match :.A at CA <http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users> :.B at CA <http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users> move false show true" But it gives the rotation angle. As I am comparing the different homologous structureswhere chain B shows more identity but the each structure have a different state giving a unique angle between chains. What can be best option to measure this??? best Jiri