Kinds of Polygraph Machines
When interrogating a crime suspect, the first thing that an investigator attempts to establish is if the person is telling the truth. The polygraph machine is the equipment of choice for law enforcement agencies as it monitors certain characteristics of the individual hooked up to the device. The machine has three general types, with varying levels of accuracy, namely the analog, computerized and hand-held devices.
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Analog Polygraph
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When polygraph technology wasn't too advanced, analog polygraphs were the devices used for interrogations. Polygraph accuracy was moderately high, as the machine takes into account a person's heart rate. A sudden swing on the graph indicates a lie, since people--in general--tend to get nervous and anxious when skirting away from the truth. More advanced machines monitor a person's breathing or respiration rate.
Computerized Polygraph
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Technology was bound to advance as the years go by, and the traditional polygraph machine received a major overhaul. Computerized devices eventually replaced their analog cousins. These machines are quite comprehensive, measuring a person's heart rate, respiration rate, leg movements, and sweating--all telltale signs if the truth isn't being told. A suspect, for instance, may slip through some of the polygraph's scales, but if he fails at least one of them, doubt will spring from the interrogator's mind.
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Hand-held Polygraph
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Given the recent advancements in technology, smaller versions of the computerized polygraph were released. These devices are used for remote interrogations, in case bringing a suspect to the crime lab isn't possible. As for polygraph accuracy, a hand-held pales in comparison to a standard computerized device. However, it is good enough to expose a normal criminal. Professional liars and "chameleons" might slip through some of them, though.
Accuracy of Polygraphs
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Research states that polygraphs, even though they are effective in normal occasions, aren't infallible. There are at least a few people who have the ability to control their behaviors in accordance to the measuring scales of a polygraph machine. However, a highly advanced computerized device is pretty accurate, since the subject has to circumvent a series of monitoring equipment. More often than not, truths and lies are efficiently exposed.
Polygraph Questions
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Polygraph accuracy isn't entirely dependent on the device. The examiner or interrogator should also ask the correct questions. The scope of questioning should cover even the minutest details, leaving no stone unturned when trying to expose an interrogated party.
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