Each FAB is made of two chains, Heavy (H) and Light (L), and two domains, Variable (V) and Constant (C or C1, The heavy domain has three parts). The angle between the variable and constant domains is the FAB elbow angle. It is the angle between rotation axes, the pseudo-dyad axes, defined by aligning the light portion of each domain, on-to the heavy one.
>>>phenix.fab_elbow_angle fab_name.pdb [light=L] [heavy=H] [limit_l=107] [limit_h=113]
>>>phenix.fab_elbow_angle 7fab.pdb light=L heavy=H limit_l=104 limit_h=117
123.00
>>>phenix.fab_elbow_angle 1bbd.pdb
126.34