This study evaluated the validity of the plumb-bob method as used to determine the break of a putt. Two separate experiments were conducted to examine the consequence of violating inherent assumptions in the method. In the first experiment, a controlled putting environment was constructed to assess the plumb-bob method in determining the break of a putt, if the slope of the green was not constant from the position of the golfer behind the ball through to the hole. It was determined that if the slope of the green beneath the golfer was different from the slope between the ball and the hole, then the plumb-bob method would provide an incorrect indication of break. The second experiment examined the ability of a golfer to stand perpendicular to a slope. Half of the participants in the study deviated by +/-1.5 degrees or greater from standing perpendicular to a slope. A + 1.5 degrees error on a 1.4 m (approximately 4.5 ft) putt translates into reading an extra 0.08 m of break and a missed putt. The plumb-bob method was found to be an invalid system for determining the break of a putt.