[Chimera-users] Hydrogen labeling scheme

Hello, I am part of a computational chemistry research group that frequently uses chimera to add hydrogens to pdbs. My coworkers and I have noticed that chimera uses several different labeling schemes for hydrogens. We have been unable to determine how chimera chooses which scheme to use. Is there a way to specify which scheme to use or to know which scheme chimera will choose? Thank you, Jack Fuller