Feed the rope well and lockes up the rope just fine.
This is a really limited belay device. It is only good for lapping single pitch gym or sport routes. There is no rappeling on double ropes with this. For the price get a device than can deal with two ropes. Evan the basic beginner will out grow the use of this device in a short time of climbing. Its just stupid...
More expensive than a regular, 2-slot Black Diamond ATC? Spring for the Black Diamond Classic ATC.. It's a better buy and you'll get more use. Or spend a little more and get the BD ATC Guide or XP..