By definition, an instrument that simultaneously records two or more channels of data. The term now most commonly signifies the instrument and techniques used in the psychophysiological detection of deception, though polygraphs are also used in research in other sciences. In PDD the polygraph traditionally records physiologic activity with five sensors: blood pressure cuff, electrodermal sensors, two breathing sensors and a sensor designed to detect covert muscular movements. Some instruments also record finger pulse amplitude using a photoplethysmograph.