I think, at least what I found from that site as a pointer from this link is, that people confuse the polygraph with being a lie-detector which in truth(again based on the readings), it is not. What it is, is an agent used in an interrogation, simply put. You are being interrogated and judged on how well they think you can actually be trusted with a security clearance(along with other factors in your application). It will have you believe that they are on to you by showing your reactions to certain questions, when in reality, there is really only one person in that room that truly knows if an answer is true or false, and it is proven that it is not the person administering the examination.