This is an excellent post that shouldn't be buried without replies. This technique gives the instructor instant control at high rates while the student only gets low rates.

Probably applicable only to people who train with their own plane and radios though.

Incidentally, Tom say that in the 9C radio AUX1 is channel 7 and is assigned to VR(E) from the basic menu. It is very useful for giving the instructor real time elevator trim.