What kind of watch is this and how do you use it?

Is it a pocket watch? Is it a pendent? A lapel? A bookmark? Are you supposed to clip it on to an item of clothing, and do you wear it on the outside or inside? Or do you clip it into a piece of stationary like a note? Or is it a part of a jewelry piece and is to be worn on a chain.

A most unusual AP skeleton watch. Highly decorated with diamonds.