[phenixbb] phenix.real_space_diff_map - difference between output maps

Dear All, I am trying to use phenix.real_space_diff_map to assess "reminiscent" density in a 1.9 A cryoEM map. Can someone explain the difference between map_model_difference_1.ccp4 and map_model_difference_2.ccp4 that PHENIX outputs? Thanks in advance, best, Jose --