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9. The origins of polygraph examination have been traced back to the efforts of Lombroso, a criminologist who experimented with a machine that measured blood pressure and pulse to assess the honesty of persons suspected of criminal conduct. His device was called a hydrosphygmograph. A similar device was used by psychologist William Marston during World War I in espionage cases, which proved to be a precursor to its use in the criminal justice system. In 1921, John Larson incorporated the measurement of respiration rate and by 1939 Leonard Keeler added skin conductance and an amplifier to the parameters examined by a polygraph machine.