I have put together a short video of how to lower a climber past a knot, if using a large HMS carabiner. This might be helpful if you have an injured climber a long way up a cliff, as with two 60 metre ropes you can potentially lower just over 120 metres. This would get you off most UK cliffs. Similarly if your rope becomes damaged you can lower off someone who can’t abseil past a knot, by isolating the damage by tying a knot.