Can you replace the question mark with a number?

A man without medicare or medical insurance injured himself playing tennis and couldn't afford to go to the doctor. A friend of his told him there was a wonderful new diagnostic machine at the drugstore and suggested he try it out.

So the man went down to the drugstore and poured the required urine sample into the machine. The machine whirred and hummed for fifteen seconds and spit out a piece of paper. The piece of paper said: You have tennis elbow. Here's how to treat it...

The man treated his tennis elbow according to the directions and it improved immediately. He was very impressed with the diagnostic machine but decided he was going to find out just how good it was, and if it could be fooled.

So he gathered and mixed together his own urine sample, his wife's, and some of his dog's feces. Then for good measure he masturbated into the cup.

He took this mixture down to the drugstore and poured it into the machine. The machine then whirred and hummed for five minutes. Just when he was thinking he'd broken it, out came the diagnosis.

It said:

Your dog has worms.

Your wife is pregnant, but don't worry, it's not yours.

And if you don't quit jerking off, you're never going to get rid of that tennis elbow.