I have been praying the LOTH for a few months now. I print off the liturgy from divineoffice.com. Since I now regularly pray it I have decided I want to get one of the books. Besides I am spending quite a lot of money on printer ink and am using a lot of paper. My question is what is the difference between the 4 volume VS. Christian Prayer VS. Shorter Christian Prayer? I believe the local Catholic store carries all three of these and I wanted to know the differences.