This technique is employed by many scratch golfers to help determine the direction and amount of break in a putt as well as the general slope of the green.

Determine your 'dominant' eye. Alternately close your eyes. The flag will remain in the circle with the dominant eye and 'pop' out of the circle with the weaker one.

Allow the club to 'hang' freely.

Hole to the left means the putt will break left. Hole to the right means the putt will break right. Hole in the center means a straight putt.