Interestingly, that was the first thing the instructor had us do, to see if we were starting our putts on line. And he showed us the Pelz Tutor with the steel balls, and the two tees method. I use a line on the ball and I think I do well with that. I started doing that last year. Before I did that, I discovered that I was aiming several inches off on a ten footer. I discovered that at home. I aimed a putt, then without moving the putterhead at all, I placed a framing square against the putterhead. If you have an assistant it would be easier to do that. Then step back and look along the edge of the square to see where it is aimed. Shocking. When I first starting using the line on the ball, my brain could hardly handle the aim it was seeing. "This CANNOT be aimed at the hole!"