What did I buy?

Hey everyone. I found this on eBay, and because I have an addiction to rotary tables I bought it. It was advertised as a Deckel tilting indexing chuck, didn’t have a size referenced in the ad. It seemed kind of small when I received it, I was hoping someone would have more information on what it’s main purpose was. Chuck measures 4”, the base can pivot from 0-90 degrees.
Thanks in advance!