From Arbo school 10 years ago!
We worked in 2 groups, 1 tree each. That was the other groups tree.
I did most of the climbing, felling out a big lightning struck(?) head, and felling the trunk of my groups tree, but i think those pics are at work. I'll try to find em too.
What i think most are missing here is that it allows you to fell almost
any width trunk.
You plunge out the vetical parts from both sides first.
Then, instead of cutting in towards your back cut square on, you put the tip in and plunge a bit to the desired depth to match up with the vertical back cut, then just keep going across the width of the trunk. You do this twice obviously.
Even if your vertical plunges dont reach each other in the middle, once you knock out each side that is fully cut, the middle only being held by vertical fibres will knock out roughly with an axe.
So with a 25" bar you could put in a 25" plunge from each side into an 80" log and knock out the inner 30"