Vimdiff with multiple buffers

I can run vimdiff with multiple files, but I'd like to be able to use
vimdiff's "do", "diffu" features.
When I try to run "do", it gives me (obviously) an error:
"More than two buffers in diff mode, don't know which one to use"

If I have 3 files, and I'm on the center one, how do I tell it to "do"
the one on the left vs the one on the right?
Or does vimdiff only work with 2 files?

Thanks,
Ven

--
--
You received this message from the "vim_use" maillist.
Do not top-post! Type your reply below the text you are replying to.
For more information, visit http://www.vim.org/maillist.php

---
You received this message because you are subscribed to the Google Groups "vim_use" group.
To unsubscribe from this group and stop receiving emails from it, send an email to vim_use+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.