This device has really helped my stroke & showed my flaws in my stroke. Worth every penny IMO. I was missing the 3rd Eye & Joe sent me one at no cost! This device shows you if your stroke is off to the left or right. It shows you where dead center ball is on the cueball. Guess what? My aim was to the left of dead center because of my eyes. This caused each stroke to impart english on each & every stroke I made. Not a good situation for me. It does take a little effort & practice but, it will pay off in the long run for anyone. It is a great product IMO.:thumbup: