An Overseer music box on a dummy.
Music Box is a written note found in Dishonored.
Transcript
Overseer Humphrey,
I left you a copy of The Ancient Music so you might familiarize yourself with the principles I’m employing in this latest variation of Holger’s Device, or the “music box” as the men call it. As you should know, it produces harmonies that render heretical energies or “magic” inert through counter-balancing mathematical principles. Read the book and then make yourself useful by finding us some subject to test it on. This city is choked with corruption and superstition, so I trust you won’t have to look far.
Signed,
Location
It can be found in the locked workshop in the Back Yard during the High Overseer Campbell mission.