I picked this up a number of years ago for reasons that entirely escape me. It's certainly neat, but I don't see myself ever actually using it and it's large and heavy.
Documented here: http://bitsavers.trailing-edge.com/pdf/fps/7259-02_AP-120B_procHbk.pdf Mine appears to have a DEC-style interface but I'm unsure what it talks to on the DEC side of things. I can take pictures if there's interest, but it's fairly nondescript, just a large white box with rack-mount ears and a small panel with some switches on it. It's in the Seattle area if anyone wants it, and it's free! Shipping is... not something I really want to think about right now. - Josh