"Another way to see this is to hold a slim paperback or sheet of cardboard angled at a tilt towards a line on the floor. Hold this flat-but-tilted plane between thumb and forefinger at each top corner and then move the left corner straight at the line on the floor while moving the other corner straight away from the line. The top corners are like the shoulder sockets. Teeter-totter the card or book back and forth and watch to convince yourself that both bottom corners stay right on the line and never swing inside the line. "

this may help otehrs to better understand your method.
Do the above exercise and hold the book about one inch for the straight edge of a desk. Move your shoulders in different directions to understand the results.
Only one movement (rocking the lead shoulder straight down) keeps the book parallel to the desk. Thanks Geoff

Thanks for the idea. I think it helps capture the feeling of moving the two sockets as if the shoulder sockets are round weights on a dumbell, with the center of bar near the base of the neck (clavicle). Remember that the center of the bottom edge of the book would represent the putterhead.

Cheers!

Geoff Mangum
Putting Theorist and Instructor
The PuttingZone.com
http://puttingzone.com
Golf's most advanced and comprehensive putting instruction.