This is the rare but legendary ADR Pan Scan stereo panning device. If you've used the Soundtoys Pan Man plug-in, it might look familiar.
Surprise, surprise - this is way more fun to use than the plug-in. It also doubles as a tremelo if you use only one channel.
The unit has great features, including width of the stereo spread, speed of the side-to-side panning, and even a L/R tilt. The coolest feature is the external trigger, where you can send a metronome signal into the trigger input and sync the panning with your hot jam.
These things are pretty darn rare, and this one's in pretty darn good shape.
