A smart engineer had managed to build a device which solely from a urine sample could diagnose any illness. Proud of his invention he persuaded a friend of his to test the machine.
The friend doubted if the machine indeed would work, but had a pee in a cup anyway. The machine processed the sample for a while, and returned a result on a piece of paper: "A tennis elbow".
"No ****ing way" the man thought and tried again with the same sample. The machine returned the same diagnose again, "tennis elbow."
Not wanting to be outsmarted by a machine the man decided to collect urine samples from his wife, daughter, poured a little motor oil in the mix and finally had a wank in the cup.
The machine processed the sample now for a little longer and returned a result: "Your wife has gonorrhea, your daughter is pregnant and your cars drive shaft will break any day now."
"And if you don't stop the wanking, your tennis elbow will only become worse!"