Some golfers like myself plumb bob most putts. I find that it confirms my original vision of the line of putt and adds information useful in my putting.  When I do my pre shot routing in putting it includes plum bobbing. You must know which your dominant eye is in order to be able to plumb bob. To determine which your dominant eye do the following: Hold your thumb to an object at a distance.  Look at the object with each eye separately.  The eye that makes the thumb move away from the object the least amount is the dominate eye. Now you are ready to plum bob.

• Stand behind your ball so that the hole, the ball and your dominant eye are aligned.
• Extend your arm slightly and hold the grip of the putter lightly between your thumb and forefinger allowing it to dangle freely in front of you.  
• Have the shaft of the putter intersect the ball and the hole.  The ball will be at the bottom of the shaft and the hole at the top of the shaft.  
• Now keep only your dominate eye open and look up at the hole to see at which side of the shaft the hole appears.
• Does the hole appear to be on the left or the right side of the shaft? If the hole is on the left of the shaft then the break is from right to left. If the hole appears on the right then the putt will break to the right. If it appears directly behind the shaft then the putt is a straight putt.