Quiltgranny

You insert it into the slot right below the dial for lowering the feed dogs, then use your right leg to operate it and your left leg for the foot pedal.

Here's a pic and some info for you. Scroll down just a bit to the second picture. The info is just to the left of it.

http://www.free-guitar-tablature.com/Bernina830.html

I have two Berninas, a 730 Record and a 1090 and I use them all the time. Most helpful, especially when appliqueing and using your walking foot while quilting.

Hope this helps,