The only thing I can think of is to keep a post it note in the cover and keep track of the last location read. Before you switch off, just take a look where you left off. Then, you can go to location and it will take you to that spot.
That's the only thing I can think of. Maybe someone else has a better idea. (It is nearly 2 AM, and I'm kind of brain dead)
Oh, and Welcome to KindleBoards. You should go over to the Introductions thread and introduce yourself..We don't bite..much.
You could add a note to the place where you stop and write something like, "Chris ended here 03/15." Or shorten it to "C 03-15." If you both do that, then it would be easy to tell where each of you last stopped.
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