The way I see it is 2b is the Humboldt and 3b is the conventional cut. The reason for the stepped notch is a precaution of the tree kicking back over the stump at you. I've seen where even 1b is now the "new" way of doing it with a 50 degree notch. The sloped cut screws you if you misjudge the lean or it sits back on you, because wedging becomes a problem and it wants to drive the wedge in a pushing motion rather than a lifting motion. I personally use the conventional because of the ease of it and I see it better than the Humboldt, but thats my personal preference and I'm not logging so it doesn't hurt my pocket book.