This knot can really help climbers out in a jam. As it can be used to belay and abseil, you can either opt to finish your climb, or abseil down and collect your belay device when you drop it down the face of the crag. Maybe after you abseil down to get it, you might consider climbing back up the rope using a pair of prussic knots?
Thanks for taking a look.
Step 1: Video.
As always please feel free to ask me any questions if you are unsure.
Step 2: Method 1
The first method that I will show you here is the method of tying it on the end of the rope.
Please refer to the pictures which I have captioned. I have done this as I think it makes it much easier to understand.
Step 3: Tying the Knot in the Middle (method Two.)
Again as with method one, I shall teach this using the pictures and notes feature on instructables as this much easier teach this way.