PP#4 is my new best friend. Tried out my 4- iron after months of collecting cobwebs. Got rid of the mythical stationary head. Had to get used to the feeling of my head tilting/rotating to the right on the backswing, while trusting that my upper body wasn't sliding. Felt like my head was sliding a couple of feet.
Anyway, on the dowswing, I felt my left side and PP#4 pulling my upper body into a very tight rotation. Tight as in no sliding, not tight as in clenching and squeezing.
Hit some great shots, with no loss of compression. Vaguely, I felt that PP#4 stayed in the same place, or at most moved very little.
Thought mostly about pivot on the downswing and hands on the backswing. Felt that my arms were "wrapping" around my body and thus also causing a very tight rotation on the backswing. ALso felt that my arms were travelling in a circular path. I may have taken the linear path of the hands too far to include my arms.
For a half hour, I felt that PP#4 monitored upper body rotation and sliding on the dowswing. I would like to know more about why it is called the Master Accumulator. I'm sure all the definitions in Webster's that HK liked to use, screams its importance.. The Commander would be PP#3, and gets all the glory .