[Chimera-users] How to display two EM map and a PBD simultaneously

Dear all, Recently, I have a task to display two EM density map ('A' and 'B') and one PDB ('C') at the same time. B and C fit in map to A. So, I need to make A and B transparent to observe them simultaneously. However, one strange thing happened when I made A and B transparent. I can only see the density which A is lager than B or B is larger than A, and I could not see the buried density. In another words, when I make both A and B transparent, the map can be changed in to the 'A+B' map, and I could not see any 'A-B' or 'B-A' information. Have anyone met this problem? Do change something in setting can solve this problem? Best regards Yang