I posted last month about this device, and showcased Radiohead's use of it in a live setting.
However now I found a video of what appears to be an older model in use, and it should be a bit more informative of the various mechanics and how it's used. It's essentially a demonstration you'd get in a music store if someone was trying to sell it to you.
Sorry if I'm killing this subject, but I find this gadget to be totally fascinating. This seems to reveal and give context to what we've heard on the radio at times from artists over the last 5-10 years.