Treetools featured a knot-based retrievable redirect YouTube clip by Dom Eastwood a few weeks ago. Drew Bristow of DB Tree followed Dom up with a video showing off his mechanical retrievable redirect a couple of days later. (Perhaps they are both laying the groundwork for the Arbor Day Arbor Camp retrievable redirect competition on Queens Birthday Weekend at the Uxbridge Reserve, North Otago?).
The DB Tree video below has Dom managing the in-tree camera with Drew demonstrating a simple O-Rig. We can't seem to get the sound to work but a picture is worth a thousand words in any case.