What the world needs now is another DIY adjustable tether. /s
Link makes it easy to tighten and capture progress. The lock/unlock is very efficient, and moving it while it's unweighted is effortless (unlike the Kong Slyde which I have been using)
Cool. If you want to geek out on endless variations of this, with clever specialized doodads for their tending, the arborists seem to come up with new ones all the time.
The RBS knot (pronounced "arbs") is named after Richard B. Schroeder, its inventor. It was quite popular before "everyone" switched to mechanical ascenders. The knot is tied by simply clipping the carabiner to the sling, spiraling the carabiner around the standing line twice, clipping the sling again, and locking the carabiner. This can be done in only a few seconds. The relative orientation of the carabiner and the standing line can take on a number of forms, but they all seem to work. The RBS knot is easily moved, but it tends to fall if unloaded. As with all carabiner knots, a locking carabiner is recommended.