I was wondering when Mooh would jump in. I have seen, first hand,(or is that third hand) his collection of partially amputated capos. If Stephan King saw them I'm sure he would be moved to write a gory thriller.... perhaps entitled "Death By Capo"
I know a group that used to,jokingly, refer to their keys as "the key of three", or whatever number corresponded with capo location. While this is meant as a joke, it also underscores the simplicity of the capo process. Breaking it all down, with respect to music theory, may be a worthwhile process, but don't lose sight of the simplicity. I think this is the capos greatest asset.
Take care. JK