There is an old story about two neighbors, a baker and a farmer. The baker began to be suspicious of the farmer, suspecting that he wasn't getting his money's worth when he paid for a pound of butter. He weighed the farmer's butter on several occasions and finally had him arrested for fraud.

The judge asked the farmer at the trial, "I presume you have scales?"

"Yes, of course, Your Honor," the farmer replied.

"And weights?" the judge asked.

"No," replied the farmer. "I don't have a set of weights."

"Then how do you hope to weigh accurately the butter you sell to your neighbor?" the judge asked.

"That's easy," the farmer said. "When the baker began to buy from me, I decided to buy my bread from him. I've been using his one-pound loaves to balance my scales. If the weight of the butter is wrong, he has only himself to blame."