How does a lie detector / polygraph?

A polygraph - also called polygraph - is a device with which one can say with some certainty whether a person is telling the truth or not. Its operation is based on the registration of different physical reactions. The reliability of a polygraph is not 100%, but now is around 70%. Read below about the methods of lie detection, the operation of a polygraph and its use. 
History of the polygraph 
A polygraph - also called polygraph - is a device with which one tries to find out the truth. The first lie detection test - also called polygraphic tests - were conducted in 1935 in Wisconsin. In the Netherlands, the first tests done on January 18, 1951 by Dr. Van der Zee (neurologist) and Dr. Holtzer (psychiatrist) in Eindhoven. 
Operation of a polygraph 
A polygraph record different physical reactions. This is done, inter alia, on the basis of electrodes. It is paid to breathing, heart rate, blood pressure, sweating, body posture, muscle tension and sudden abnormal operation. A lie detection test assumes that if a person is not telling the truth, this is accompanied by an emotion. This emotion, in turn, generates a response to in our autonomic nervous system and these reactions we can measure with the aid of, inter alia, to the electrodes. A person who is aware of the fact that he was not telling the truth, an increased heart rate, blood pressure, breathing, sweating and muscle tension.
Guilty or not? 
A lie is never 100% reliable. Depending on the measurement method and the person may be called false positives occur, which they wrongly designated as guilty, or false negatives, which they wrongly considered not guilty.Lie detectors are rarely acknowledged as strong evidence, but offer a good supplement or witness statements and DNA research. There is also criticism of the polygraph. Thus, the response to stimuli of each person differently. A psychopath reacts eg with very little physiological activity when telling a lie.