I recently signed up for 10 lessons with GOLFTEC, which includes 1.5 hours use of practice bays for each lesson.
These folks claim to have data from many hundreds of PGA TOUR pros to substantiate their various "checkpoints". Most are routine but the one new one (for me) is what they're calling "shoulder bend" at the top of the backswing. They claim the pros have 0 degrees or, even better, negative a few degrees. This category is supposedly "correlated" with maximizing "power". To achieve this position it correspondsponds to Plummer's "Spine Extension" in the DVD's which, along with Rota