A businessman was taking a chartered helicopter flight over Seattle. A thick fog bank rolled over the Puget sound. Just then, the pilot started having problems with his navigational equipment. He tells the businessman he needs to get his bearings, so he slowly lowers the helicopter towards the ground. He sees a glass office building so they slowly hover towards it. They can see someone in a window, so the pilot writes on a large piece of paper "Where are we?" and holds it up so the man in the building can see it.
The man in the building then writes his reply on a piece of paper, and holds it up to the window. It reads "You are in a helicopter".
The pilot then pulls up, and minutes later safely navigates to the airport. The businessman was impressed. "How in the world did you figure out where were?"
The pilot answers, "he gave us accurate, yet totally useless information, so I knew we were at the Microsoft headquarters."