Studies over the last few years in USA by USPGA Professional, A.J.Bonar, clearly and irrefutably show that the clubface of all top players actually closes at the rate of 2.5 degrees every inch. Simply put, this means that the clubface rotates a full 30 degrees from 6 inches before impact to 6 inches after impact! I quote from a recent e-mail from AJ;
The first measurement I made about the amount of toe rotation was about 17 years ago, and it was done when I had a company, Digital Precision Golf, measure my own clubface to find the difference in speed between the heel and the toe. The chap that owned the company thought my interest was misplaced. He thought it would not be more than 1 mph, at best. On the day following his capture of my 5 iron shot, he called me and said the toe of my 5 iron was traveling 16.5 mph faster than the heel. This seemed to me to be more in line with what I saw on the lesson tee, when students move from the "square face" impact concept to using the dynamic, rotating clubface through impact.
In 1998, I had access to an electro-magnetic technology that measured the clubface in the impact zone. It measured the face rotation, angle of attack, ball/face contact point, and speed. When we tested tour players, we noticed that the rotational function repeatedly gave us 2.5° of rotation per inch of linear movement of the heel.