The Encyclopedia of the Pivot System" by Dr. Ronald Reinhardt used to be the authority at the time it first came out and was the source most trumpet instructors went to for explanations to their students as to what happens when we played, back then. Today there are as many ideas as to what happens in the throat and mouth areas as there are new mouthpieces and horn on the market. The old school advocated a pivot and many current views disagree with this thought. Each player must decide what works and doesn't work for themselves. What players sometimes believe does not prove out in deeper investigations into the action of the jaw, tongue, throat while playing. You may find the following film helpful when you start analyzing your own playing style. What is Really Happening in Your Body When You Play Trumpet? | The Trumpet Blog Dr. Ronald Reinhardt's case histories should be required reading by for all trumpet players regardless of their own understandings.