The doughnut effect

A golfing friend recently relate to me about an interesting article that he has read on the internet:

An American NASA scientist analyzed and came to the conclusion that a flight of 4 golfers would leave more than 400 foot prints on a green during putting. Most of these foot prints are concentrated around the cup because every golfer removes his ball from the cup after putting. He does it in a certain fixed sequence of movements, usually ending with one foot in front (leaning on his putter?!) and the other foot behind him as he bends to retrieve his ball from the cup. This very posture causes the green around the hole (18" radius) to be compressed more than the rest, forming what is termed a "doughnut". In fact the grass around the hole never had a chance to recover sufficiently so that a circular impression is left permanently around the cup until its location is changed by the green keeper by digging a new hole at a new location on the green. This same doughnut will be formed around the new hole within one day.

This doughnut shaped patch of grass around the cup causes all slow putts to break to both sides near the hole so that the ball appears to avoid the hole. A golfer thinks that he has read the green incorrectly (he hasn't). We call this the doughnut effect! It has fooled many unwary golfers. To overcome this doughnut effect on the green, for short putts, we charge the hole, aiming to stop at a spot 18" behind the cup. This way, the ball does not turn sideways and away from the hole.

(contributed by Tsun Kong)