To become a great putter you have to hit the ball on the sweet spot consistently. That will give you a true roll and better distance control. However, sometimes the sweet spot is not where the manufacturer says it is so this is a great drill to find the sweet spot on your putter. I am going to tap the face of the putter with my ball and I am getting face rotation and the shaft is twisting in my hand, I can feel that. As I come towards the center of the putter it is very stable, no twisting, and then out on the heel I am getting some face rotation and twisting again. So where I feel that it is very stable I am going to check, and gosh that is perfect, it is right where the manufacturer says it is going to be. But often that stable point can be more inside towards the hozzle or shaft of the club and then you might want to make a mark on your putter so that you can use that to align your ball, hit solid putts that roll a little straight and your distance control may be better. Now the other way that you can use this method is when you go to buy a new putter. You want to test the face of the putter and make sure that the sweet spot is right where the manufacturer says it is, especially if there is a line so that you can use that mark. Some putters do not have lines so you want to test it and remember where that spot is so that you can hit the ball on the sweet spot, get a great roll and better distance control. This is really going to help your putting.