Dave is 90 years old. He's played golf every day since his retirement 25 years ago. One day he arrives home looking downcast. "That's it," he tells his wife. "I'm giving up golf. My eyesight has become so bad that once I hit the ball I can't see where it went." His wife sympathizes and makes him a cup of tea. As they sit down she says,
"Why don't you take my brother with you and give it one more try."
"That's no good," sighs Dave, "your brother's 103 years old. He can't help."
"He may be 103," says the wife, "but his eyesight is perfect."
So the next day Dave heads off to the golf course with his brother-in-law. He tees up, takes a mighty swing and squints down the fairway.
He turns to the brother-in-law and says, "Did you see the ball?"
"Of course I did!" replied the brother-in-law. "I have perfect eyesight".