MG did my test, I was actually taught by Mike Bill down at Redhill, and you're welcome to pm.
As Whirlybird says, I wouldn't sweat the diagram. As she also says, you're not going to tell your student why it autorotates at this point, just that the upward airflow through the rotor replaces the engine torque. So why make it complicated. I'm generally really crushed because I love the aerodynamics stuff (as an amateur I hasten to add) and yet I'm less and less sure it helps when teaching someone how to fly.
Re. 2 MB had a cunning diagram which is almost certainly wrong mechanically, but certainly helps to imprint the behaviour of the correlator on a student.
He drew the throttle cable as if it were wound clockwise (looking from the front) around the collective lever about six inches forward of it's pivot point. The twistgrip would therefore work as you'd expect but raising the lever would also open the throttle.
But because the collective moves in an arc its effect on the throttle in this configuration is a circular function not linear. If you draw it out (and my explanation has been OK) you can see that the movement would be relatively greater around 0 to 10 deg (from the horizontal) than say 40 to 50 degrees (ie a cosine function). Therefore the throttle overcompensates in the low range (<16") and undercompensates in the high range (> 21").
I'll admit it's not the simplest analogy, but it does work !
HTH
Last edited by puntosaurus; 6th Dec 2005 at 19:00.