This invention first was a failure by James Mackenzie in 1902, but when John Larson advanced this invention he changed what the machine studied. His machine looked at the blood pressure, pulse rate, and perspiration. On his machine pens would record the different responses of BP, pulse, and perspiration as a person asked questions. The question they asked were a pattern of true and false so they could see how the person responded to questions that were true and false. The test they took lasted for about 2 hours. After the test experts would examine the results to determine if the person was telling the truth about the crime.
The lie detector uses different wires with a rubber pad to measure rates and pulses. They place the wires in different places on the body. They place two on the waist and chest of the person to measure breathing. To measure prespiration a metal plate is attached to the person's hand. A cuff is placed on the arm to measure the heart rate and blood pressure.
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