Hi, I'm looking at the best (=fastest) way to compare a (possibly incomplete) list of observed reflections f_hkl_obs (or fo2_hkl_obs) to the f_hkl_calc of calculated structure factors or intensities from a model structure. in miller.py there is a function to calculate a difference between f_obs and f_calc, but it asserts that all reflections are present in f_obs: def f_obs_minus_f_calc(self, f_obs_factor, f_calc): assert f_calc.is_complex_array() assert self.indices().all_eq(f_calc.indices()) assert self.anomalous_flag() is f_calc.anomalous_flag() ... In my case it's possible that some reflections could not be observed so they should either be skipped or be assumed to be of zero intensity. As I could not locate the definition for .all_eq(...), yet I'm not sure if this is already handled and if it is how it is done. Then there is f_obs_minus_xray_structure_f_calc in miller.py as well. Would this be a better approach if the model structure changes quite often? What if I just got f_calc from another source (like doing some custom sped-up partial structure factor calculation)? In general: What would be your advice on this with cctbx? With regards, Dipl. Phys. Jan M. Simons Institute of Crystallography RWTH Aachen University