Pistol - you wrote-: "The problem i see here is it depends on the definition of when a backswing has finished and a downstroke has started ..Kinetic Link may have a different view on this opposed to TPI..and which player is tested."
Your belief about different definitions of the end-backswing may be true, and that's why I believe in standardised definitions. Cheetham, of TPI, has recently accepted what I regard as the only scientifically-supportable definition for the end of the backswing - when the club changes direction. All the latest TPI graphs now use that strict definition for the top/end of the backswing - rather than vague criteria eg. when the shoulders stop turning or when the pelvis reverses direction and starts to move forward (a phenomenon which actually may occur during the backswing in many good golfers).
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