In issue 48 of Qi Magazine, there is an article about Wu Style Tai Chi Master Wang Hao Da. The article describes Master Wang's early training and his desire to interact with as many different people as possible to refine his art.

The description of Zhong Ding, or Central Equilibrium, drawn from the article, explains much of what organized Master Wang's teaching and personal practice, as described to me by one of my teachers, Robert Tangora.

Correct central equilibrium {Zhong Ding} is the basis for everything else in Taijiquan. One must focus with their complete intention {Yi} to differentiate that which is external and separate from one's centre. The centre is the key; it must remain straight and hidden, concentrated, deep inside the body constantly changing, spiraling into the earth for the most part. One must gather all the Qi {energy} to your centre. It is this structure that is the basis for internal power {Nei Jing} or Zhong Ding Jing, and essential for good health and longevity. The Dantien {lower abdomen} is alive! Not only does the Dantien push down inside the open hips but also it turns, spirals, bounces, and shoots; inside the structure is always full, always condensed. When you play the Taiji form you are performing the interaction of your Zhong Ding and Dantien. This hidden internal play moves the outside, not necessarily the entire body like a single lump of wood, rather by gathering everything to your centre, your outside body follows the direction of this internal command. It is because your inside works so intensively that you receive the health benefit of Taiji. If one only works externally and has strong skin and muscles but weak organs, vessels, and bones, then the outside may thrive while internally you are dying.

If you understand the importance Master Wang placed on Zhong Ding, you can begin to understand the nature of his unique-looking form:

The sharp bursts sprinkled throughout the form are caused by the sudden release of energy from his Zhong Ding. The rest of the time he is actively gathering into the Zhong Ding, focusing his mind there and letting all the physical movement feed the sense of gathering and storing.

We worked on a basic version of this exercise in preparation for Tai Chi Cloud Hands.