polygraph lie detector test pretoria, gauteng, south africa


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Polygraph Instrumentation


A polygraph examination is a helpful tool in any investigation or in a case where there is no other way of establishing facts. Our aim is to provide professional, experienced and accredited polygraph services that are based on validated techniques that are in accordance with internationally accepted standards.


Some new users of the polygraph technique refer to this technique as "lie detection". The polygraph is not a lie detector! Polygraph refers to two things namely: "poly" meaning many and "graph" meaning to write. It therefore refers to the many writings the instrument makes that indicate whether or not someone is telling the truth.

Analogue Polygraph Chart    Digital Polygraph Chart


"Polygraph" in the sense in which it is normally used refers to mainly two things namely the technique applied and secondly the instrument used for such purpose. As the majority of lie detector examinations performed in South Africa yield results of non-deception it should rather be called a "truth detector" instead of "lie detector".


"Graph" in the word means the graphical display of tracings representing functions of the body when someone is answering a question. This means it is an instrument that is used to measure and record certain responses coming from the body when someone is asked questions to indicate whether or not he or she is telling the truth.


These physical reactions happen whether or not the instrument is attached or used. Whenever there is a measure of fear created by the question to which a person is responding, the responses that are recorded are produced in the examinee. Such fear may relate to imprisonment and loss of position etc. The fact that it is a forensic technique means it may be used as scientific evidence in hearings or in court trials.

Polygraph examination
The polygraph is an instrument that simultaneously measures thoracic and abdominal breathing patterns, relative changes in blood volume and the resistance of electricity in sweating. During the polygraph examination, the examinee is connected to the instrument and then monitored to see how that personís body reacts based on those parameters when being asked questions.


It is important to understand what a polygraph examination entails. A polygraph instrument will collect physiological data from at least three systems in the human body. Convoluted rubber tubes that are placed over the examinee's chest and abdominal area will record respiratory activity. Two small metal plates, attached to the fingers, will record sweat gland activity, and a blood pressure cuff, or similar device will record cardiovascular activity.


It is better to refer to this technique as forensic psycho-physiological detection of deception. Basically it is the same technique that has been in use since 1896. It has been refined and now uses a sophisticated instrument, question techniques and a trained and experienced Examiner determining the truth reliably.


Historic polygraph machine

Analogue Polygraph

Historic image of polygraph examination


The name refers to the manner in which selected physiological activities are simultaneously recorded. Polygraph examiners may use conventional instruments, sometimes referred to as analogue instruments, or computerized polygraph instruments.


A typical polygraph examination will include a period referred to as a pre-test, a chart collection phase and a test data analysis phase.


In the pre-test, the polygraph examiner will complete required paperwork and talk with the examinee about the test. During this period, the examiner will discuss the questions to be asked and familiarize the examinee with the testing procedure.


During the chart collection phase, the examiner will conduct and collect a number of polygraph charts. Following this, the examiner will analyze the charts and render an opinion as to the truthfulness of the person taking the test.


The examiner, when appropriate, will offer the examinee an opportunity to explain physiological responses in relation to one or more questions asked during the test.


It is important to note that a polygraph does not include the analysis of physiology associated with the voice. Instruments that claim to record voice stress are not polygraphs and have not been shown to have scientific support. The video below is a prime example of the difference between a polygraph and voice stress instrument.






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