Keeping track of direction when fishing
The next day Johnny and his pal went fishing in the Gulf. The fish were plentiful and in no time they had a boat load. Came the next morning, and the two men went fishing again. This time they caught nothing at all.
"Say, Johnny," asked the friend, "are you sure we're in the same spot we came to yesterday?"
"I certainly am," answered Johnny. "I even marked the place."
"You did?" said the friend, looking around. "I don't see anything in the water."
"Oh, I didn't mark the water," said Johnny. "See over here" -and he pointed out a big X-"I marked the side of the boat!"