Interestingly, in addition to the manifold pressure (sort of equates to torque) and tachometer, the Schweizer 300CBi's I trained in also had a rivet in the slide plate, which formed a part of the collective friction mechanism. I asked what it was for. I was told that if you continued to pull collective, the friction discs would bump up to the rivet, that was a tactile indication that you were probably in the MP limiting range of power. But, you could continue to pull, and the friction discs would pass the rivet, and you could pull more if you needed to. A crude system, but it seemed to work. I only felt the contact with the rivet a couple of times, and never felt the need to pull past it.