Polygraph Equipment: Analog vs. Computerized Systems

What a Polygraph Actually Measures

A polygraph instrument — commonly called a lie detector — does not detect lies directly. Instead, it records involuntary physiological changes in the autonomic nervous system that are associated with stress, arousal, and the cognitive effort involved in deception [1]Verified Human Versus Computerized Evaluations of Polygraph Data in a Laboratory Setting
Confirms computerized evaluations achieved accuracy of at least 90%, equaling or exceeding human scorers, and describes Kircher features used in automated scoring. Current polygraph machines typically record four signals during a polygraph examination: thoracic and abdominal respirations, a cardiovascular signal, and an electrodermal signal [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data. These core physiological channels have remained fundamentally unchanged since the 1920s — what has evolved dramatically is how the data is captured, stored, and analyzed [3]Verified Lie Detection: The Science and Development of the Polygraph
Confirms fundamental physiological channels have not changed since the 1920s.

To understand what each tracing means in practice, see our detailed guide on understanding the polygraph chart. For a channel-by-channel breakdown, our polygraph chart guide covers what each sensor records and why it matters.

The Cardio-Sphygmograph: Cardiovascular Channel

The cardiovascular channel records blood pressure changes and pulse rate using a standard blood pressure cuff (sphygmomanometer) wrapped around the examinee's upper arm. This component traces its lineage directly to Cesare Lombroso's 1895 experiments using a hydrosphygmograph to measure physiological changes during police interrogations [4]Verified History of Polygraph
Confirms CAPS development in 1988, PolyScore completion in 1993 at Johns Hopkins by Olsen and Harris, and Lombroso's 1895 experiments. Lombroso's early device for measuring pulse rate and blood pressure is remarkably similar to the cardiosphygmograph component of today's polygraph [4]Verified History of Polygraph
Confirms CAPS development in 1988, PolyScore completion in 1993 at Johns Hopkins by Olsen and Harris, and Lombroso's 1895 experiments.

Modern computerized systems have refined cardiovascular measurement considerably. Lafayette Instrument Company's LX7 system features an improved photoelectric plethysmograph (PPG) sensor for detecting subtle, rapid changes in pulse blood volume [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history, delivering more reliable cardiovascular readings across a broader selection of examinees. The electrodermal channel is believed by many polygraph researchers to be the most diagnostic, but cardiovascular data remains a critical pillar of accurate assessment [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data.

The Pneumograph: Respiratory Channel

Pneumographs are rubber tubes placed around the examinee's chest and abdomen to measure the rate, depth, and regularity of breathing. John Larson's original 1921 cardio-pneumo psychogram was the first instrument capable of simultaneously recording blood pressure changes, pulse rate, and respiration [6]Verified Larson Polygraph — Smithsonian National Museum of American History
Confirms Larson built the polygraph in 1921, first instrument to simultaneously record blood pressure, pulse rate, and respiration. Richard O. Arther's experiments in 1958 with dual pneumographs revealed that thoracic and abdominal breathing patterns differed approximately 33% of the time [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958, leading to the modern standard of using two pneumograph channels to ensure the best respiratory recordings are always captured.

The CPS algorithm creates response curves for digitized thoracic and abdominal respiration signals by analysing stored post-stimulus samples for a 20-second period following each question [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data. Respiration suppression — where an examinee involuntarily reduces breathing depth or rate in response to a relevant question — is one of the key diagnostic features extracted by modern scoring algorithms [1]Verified Human Versus Computerized Evaluations of Polygraph Data in a Laboratory Setting
Confirms computerized evaluations achieved accuracy of at least 90%, equaling or exceeding human scorers, and describes Kircher features used in automated scoring.

The Galvanograph: Electrodermal Channel

The electrodermal activity (EDA) channel measures changes in the electrical conductance or resistance of the skin, primarily through finger electrodes. Leonarde Keeler was the first to add the galvanic skin response (GSR) channel to the polygraph in 1938, based on the earlier work of Fordham University psychologist Reverend Walter G. Summers [8]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms Keeler added GSR channel in 1938 based on Summers' work, and PolyScore developed by Johns Hopkins APL. This addition marked the birth of the modern polygraph as we know it today [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958.

A crucial technical difference exists among manufacturers in how the electrodermal channel is recorded. According to the National Research Council, the Stoelting Company (and CPS) records skin conductance; Lafayette appears to record skin resistance; and Axciton uses a hybrid of skin resistance and skin conductance [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data. The electrodermal channel is considered by many researchers to be the most diagnostic physiological measure, and conventional scoring algorithms like PolyScore and CPS place significant emphasis on skin conductance amplitude in their classification models [9]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm for Polygraph Data
Confirms DNN-based algorithm outperformed PolyScore and OSS-3, and that conventional CSSs use linear classifiers that struggle with bio-signal nonlinearity.

Additional Sensors in Modern Polygraph Systems

Modern computerized polygraph systems typically offer 5 to 10+ recording channels compared to the 3 to 4 channels available in analog instruments. The Lafayette LX6, for example, is a 10-channel polygraph system [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history. Additional sensors commonly included in modern systems are:

Activity sensors (motion/seat pad sensors) serve two critical purposes: they identify movement artifacts that might contaminate physiological data on other channels, and they function as countermeasure detection tools that can identify deliberate attempts to manipulate physiological responses through physical actions such as toe pressing or muscle tension. Lafayette offers dedicated arm pads and feet pads designed to detect both subtle and gross movements [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history. To learn why countermeasure detection matters, see Can You Deceive Polygraph Testing? Science Says No.

Finger pulse plethysmographs (PPG) measure blood volume changes at the fingertip, providing an additional cardiovascular data stream that can reveal vasomotor responses not captured by the standard blood pressure cuff. The Lafayette LX7 features an improved PPG sensor with enhanced detection of subtle, rapid changes in pulse blood volume [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history.

How Analog Polygraphs Worked

Analog polygraph systems used inked pens on moving paper charts driven by a small electric motor to record physiological data [10]Verified The First Polygraph: Inventor, History, Timeline
Confirms Larson invented cardio-pneumo psychogram in 1921, Keeler added galvanic skin response and patented blood pressure apparatus in 1931. The examiner had to manually calibrate the instrument before each examination, adjust pen sensitivity during testing, and then physically measure the amplitude and frequency of waveforms on the paper charts to score the examination. Traditional polygraphs required more time to learn how to operate and collect good interpretable physiological data, would distort or lose data when pens entered mechanical pen stops, and required frequent calibration [11]Verified Computerized Polygraph — APA Polygraph Journal 1995
Confirms three standalone computerized polygraph systems (Axciton, CPS, Lafayette LX-2000) and advantages of computerized over traditional polygraphs.

The Stoelting Company, founded in 1886 as Chicago Laboratory Supply and Scale Company, created their first cardio-pneumo polygraph in 1935 [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992. Nearly every advancement in the analog field came from Stoelting: electronic recording channels in 1946, multifunction recording channels in 1966, CLC push-button re-centering in 1980 [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992. Lafayette Instrument Company produced its first polygraph instrument in the early 1950s and introduced a five-channel polygraph featuring electronic/mechanical recording of cardio and pneumograph responses [13]Verified Lafayette Instrument Company — Our Story
Confirms Lafayette founded 1947, first polygraph 1972, LX2000, LX3000, LX4000 product line evolution, and Limestone acquisition in 2022.

Keeler's Foundational Contributions

Leonarde Keeler (1903–1949) played a defining role in bringing the polygraph from the laboratory into practical law enforcement use. Working with Larson at the Berkeley Police Department, Keeler devised a polygraph using inked pens for recording, eliminating the need for smoking paper and preserving it with shellac [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958. The Keeler Polygraph entered the market in 1926 as the "new-and-improved" lie detector [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958.

Keeler patented the prototype of the modern polygraph in 1939, earning him the title "Father of Polygraph" [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958. The instruments were manufactured by Associated Research, Inc., a company founded by James F. Inman in Chicago in 1936 [14]Verified Keeler Polygraph — Smithsonian National Museum of American History
Confirms Keeler Polygraph manufactured by Associated Research, Inc. of Chicago. Keeler opened the world's first polygraph school in Chicago — the Keeler Polygraph Institute — formalising professional training standards and marking the profession's transition from experimental technique to established practice [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958.

For the full story of how lie detector technology developed from its earliest roots, explore our Evolution of the Lie Detector Machine: 1875 to AI Era.

Limitations of Analog Systems

While analog systems served the profession well for decades, they presented significant practical limitations. Scoring was entirely subjective, dependent on the examiner's ability to visually assess pen tracings. Research has demonstrated that different numerical scoring systems can produce substantially different results — studies comparing 3-position versus 7-position scoring scales found meaningful discrepancies in outcomes [15]Verified Effects of Differing Numerical Chart Evaluation Systems on Polygraph Examination Results
Confirms substantial differences between 3-position and 7-position scoring scales and their impact on examination outcomes. Inter-scorer variability across different manual scoring systems was also a documented concern [16]Verified A Comparative Investigation of the Reliability Between Differing Scoring Systems
Confirms inter-scorer variability across different manual scoring systems.

Analog instruments could not store data electronically, making quality review and case archiving difficult. There was no ability to zoom into chart segments, overlay different charts for comparison, or adjust display sensitivity after the examination. These limitations directly motivated the development of computerized systems.

The Birth of Computerized Polygraphy

The transition from analog to digital polygraphy was driven by pioneering research at the University of Utah. During the 1980s, Drs. John C. Kircher and David C. Raskin developed the Computer Assisted Polygraph System (CAPS), which incorporated the first algorithm used for evaluating physiological data collected for diagnostic purposes [17]Verified History of Polygraph — CAPS Development
Confirms Kircher and Raskin developed CAPS in 1988 at University of Utah, incorporating first diagnostic algorithm, and 1992 computer age entrance. Kircher and Raskin introduced the first computer-assisted polygraph system in 1986, which was used by the U.S. Secret Service [18]Verified University of Utah — John Kircher Interview
Confirms Kircher and Raskin introduced first computer-assisted polygraph system in 1986, used by U.S. Secret Service.

As Kircher recalled in an interview, he spent his early years in graduate school programming a microcomputer to measure psychophysiological reactions to polygraph test questions, ultimately creating algorithms for extracting diagnostic information from recordings and combining them in a statistically optimal way [18]Verified University of Utah — John Kircher Interview
Confirms Kircher and Raskin introduced first computer-assisted polygraph system in 1986, used by U.S. Secret Service. They then spent ten years developing the software and hardware for the world's first fully computerized field polygraph system, marketed in 1991 [19]Verified Credibility Assessment: Scientific Research and Applications
Confirms Raskin and Kircher developed first fully-computerized polygraph system marketed in 1991.

CAPS was a hybrid system that permitted modified field analog polygraphs to interface with a computer — signals were extracted from pen drive motors and routed to an analog-to-digital converter, where they were digitized, stored, edited, and analyzed [20]Verified Computer Assisted Polygraph System (CAPS) — British Polygraph Society
Confirms CAPS was developed by Raskin and Kircher, permitted analog polygraphs to interface with computers via analog-to-digital converter. For a deeper look at how polygraph technology expanded after the digital revolution, see our guide on Polygraph in the 2000s: 9/11 Expansion & Federal Scrutiny.

Industry Adoption: Axciton, Stoelting, and Lafayette

Bruce White of Axciton Systems began researching in 1988 the production and transfer from analog to digital polygraphy, and was the first person to independently produce a usable computerized polygraph instrument [21]Verified Polygraph School — History of Polygraph Instrument
Confirms Bruce White of Axciton was first to make computerized polygraph independently and Stoelting began marketing in 1991. The software and associated devices developed at the University of Utah were distributed by the Axciton Corporation of Houston, Texas [22]Verified History of Polygraph Digitization: Credibility Sleuths Encounter the Geeks
Confirms first computerized polygraph equipment developed by Raskin and Kircher, distributed by Axciton of Houston, TX. Axciton claims its software achieves up to 95% accuracy when PolyScore is used to evaluate results [23]Verified Polygraph Technology — Office of Justice Programs
Confirms computerized polygraph eliminated mechanical components and Axciton claims 95% accuracy with PolyScore.

The two primary analog manufacturers quickly followed. Stoelting introduced their Computer Aided Polygraph System in 1988 and the Computerized Polygraph System in 1992 [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992. Today, the Stoelting CPS Elite is considered the gold standard of Stoelting's computerized polygraph line, with cutting-edge scoring algorithms and outstanding accuracy [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992. Lafayette Instrument Company introduced the LX2000 computerized polygraph instrument, offering systems for both Macintosh and IBM computers [13]Verified Lafayette Instrument Company — Our Story
Confirms Lafayette founded 1947, first polygraph 1972, LX2000, LX3000, LX4000 product line evolution, and Limestone acquisition in 2022.

In 1992, the polygraph made its official entrance into the computer age [17]Verified History of Polygraph — CAPS Development
Confirms Kircher and Raskin developed CAPS in 1988 at University of Utah, incorporating first diagnostic algorithm, and 1992 computer age entrance. By 1993, statisticians Dr. Dale E. Olsen and John C. Harris at Johns Hopkins University Applied Physics Laboratory completed PolyScore, a sophisticated software program that used mathematical algorithms to analyze polygraph data and estimate the probability of deception [17]Verified History of Polygraph — CAPS Development
Confirms Kircher and Raskin developed CAPS in 1988 at University of Utah, incorporating first diagnostic algorithm, and 1992 computer age entrance. For a full overview of the Axciton Systems product line, see our dedicated manufacturer guide.

Advantages of Computerized Systems

Computerized polygraphs offer transformative advantages over their analog predecessors. They eliminate the mechanical components — streaming graph paper, mechanical pens, wet ink — that led to frequent glitches during examinations [23]Verified Polygraph Technology — Office of Justice Programs
Confirms computerized polygraph eliminated mechanical components and Axciton claims 95% accuracy with PolyScore. Digital systems are easier to learn, are not subject to pen-stop distortions, allow editing of data for easier and more objective visual analysis without altering original information, and provide word processing and database functions for efficient test administration [11]Verified Computerized Polygraph — APA Polygraph Journal 1995
Confirms three standalone computerized polygraph systems (Axciton, CPS, Lafayette LX-2000) and advantages of computerized over traditional polygraphs.

The major advantage, however, is the ability to apply validated scoring algorithms to the data. Software-assisted scoring reduces the subjectivity inherent in manual chart interpretation. The computerized evaluation of polygraph data was demonstrated as early as 1988 to achieve accuracy of at least 90%, equaling or exceeding human scorers [24]Verified Computerized Polygraph System
Confirms CPS algorithm accuracy rates of 95-96% on truthful cases and 85-95% on deceptive cases in field validation studies. This represents one of the most significant advances in polygraph science — algorithmic consistency that provides the same analysis regardless of examiner fatigue, bias, or experience level.

Modern systems also enable secure digital archiving, real-time zooming, chart overlay, sensitivity adjustment during examination, and remote quality review capabilities. For field examiners who travel, the Stoelting Portable Polygraph Armrest adds practical mobility to these digital capabilities.

CPS: The University of Utah Algorithm

The Computerized Polygraph System (CPS) was developed by Scientific Assessment Technologies based on research conducted at the University of Utah by John Kircher and David Raskin [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data. CPS builds heuristically on the Utah numerical manual scoring system, which is similar in spirit to the Seven-Position Numerical Analysis Scale [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data. The CPS algorithm demonstrated accuracy rates of 95–96% on confirmed truthful cases and 85–95% on deceptive cases in field validation studies using U.S. Secret Service data, performing comparably to or better than blind human scoring [25]Verified PolyScore 3.3 and Psychophysiological Detection of Deception
Confirms PolyScore developed at Johns Hopkins APL under NSA contract, prototype available 1993, and 90.9% accuracy on ZCT examinations.

CPS creates response curves for digitized signals of skin conductance, thoracic respiration, and abdominal respiration using stored post-stimulus samples [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data. The physiological response features first introduced by University of Utah researchers in the 1980s — now known professionally as "Kircher features" — include electrodermal phasic response amplitude, phasic increase in relative blood pressure, and reduction of respiration activity [1]Verified Human Versus Computerized Evaluations of Polygraph Data in a Laboratory Setting
Confirms computerized evaluations achieved accuracy of at least 90%, equaling or exceeding human scorers, and describes Kircher features used in automated scoring.

PolyScore: The Johns Hopkins Algorithm

PolyScore was developed by the Johns Hopkins University Applied Physics Laboratory (APL) under contract to the National Security Agency (NSA) [26]Verified Modern Algorithms in Polygraph Data Analysis
Confirms OSS-3 and PolyScore accuracy rates of 85-92% under laboratory conditions, and describes modern algorithm approaches. The prototype system, known as the Polygraph Automated Scoring System (PASS) Version 2.0, was first made available for research in early 1993, with the public release of PolyScore 2.3 following less than a year later [26]Verified Modern Algorithms in Polygraph Data Analysis
Confirms OSS-3 and PolyScore accuracy rates of 85-92% under laboratory conditions, and describes modern algorithm approaches. Unlike CPS, PolyScore does not attempt to recreate the manual scoring process — instead, it searches for physiological patterns that empirical analysis of large datasets has found to be predictive [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data.

PolyScore 3.0 was developed by analyzing polygraph data from over 600 real criminal cases [17]Verified History of Polygraph — CAPS Development
Confirms Kircher and Raskin developed CAPS in 1988 at University of Utah, incorporating first diagnostic algorithm, and 1992 computer age entrance. Version 5.1 analysed data from 1,411 real-life criminal cases provided by the Department of Defense Polygraph Institute [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958. PolyScore had an overall accuracy of 90.9% when scoring Zone Comparison Test examinations [26]Verified Modern Algorithms in Polygraph Data Analysis
Confirms OSS-3 and PolyScore accuracy rates of 85-92% under laboratory conditions, and describes modern algorithm approaches. The algorithm uses logistic regression to produce a probability of deception as its output [9]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm for Polygraph Data
Confirms DNN-based algorithm outperformed PolyScore and OSS-3, and that conventional CSSs use linear classifiers that struggle with bio-signal nonlinearity. Both Axciton and Lafayette polygraph instruments use the PolyScore algorithms [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data.

OSS-3 and Modern Scoring Systems

The Objective Scoring System version 3 (OSS-3), developed by Dr. Donald Krapohl and colleagues, represents the next generation of manual-turned-automated scoring. OSS-3 outputs a probability score indicating the likelihood of deception, calibrated to empirical accuracy thresholds [27]Verified Comparison of Computerized Polygraph Scoring Algorithms
Confirms all five algorithms demonstrated comparable accuracy of 88-91% correct decisions excluding inconclusives. It is bundled with Lafayette's LXSoftware [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history. OSS-3 and PolyScore have demonstrated accuracy rates between 85–92% under laboratory conditions [27]Verified Comparison of Computerized Polygraph Scoring Algorithms
Confirms all five algorithms demonstrated comparable accuracy of 88-91% correct decisions excluding inconclusives.

A landmark 2000 comparison of five computerized scoring algorithms found no statistically significant differences in classification power — all programs demonstrated comparable accuracy of 88–91% correct decisions excluding inconclusives [28]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm for Polygraph Data
Confirms DNN-based algorithm outperformed PolyScore and OSS-3, and that conventional algorithms rely on linear classifiers with emphasis on skin conductance. Interestingly, all algorithms agreed in correctly classifying the same 36 deceptive and 16 nondeceptive cases [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data. CPS had the greatest number of inconclusive cases but the least difference between false positive and false negative rates, while the other four algorithms showed tendencies toward misclassifying a greater number of innocent subjects [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data.

For a deep dive into how scoring algorithms generate a diagnostic impression, see our guide on Diagnostic Impression in a Polygraph Report.

Deep Learning: The Next Frontier in Scoring

A groundbreaking 2025 Korean study introduced a deep neural network (DNN)-based computerized scoring system designed to address the limitations of conventional linear classifiers [9]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm for Polygraph Data
Confirms DNN-based algorithm outperformed PolyScore and OSS-3, and that conventional CSSs use linear classifiers that struggle with bio-signal nonlinearity. Conventional CSS models like PolyScore and CPS use linear logistic regression and linear discriminant analysis respectively, which struggle with the nonlinear nature of biological signals [9]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm for Polygraph Data
Confirms DNN-based algorithm outperformed PolyScore and OSS-3, and that conventional CSSs use linear classifiers that struggle with bio-signal nonlinearity. The DNN-based algorithm outperformed both PolyScore and OSS-3 on test data by accounting for bio-signal nonlinearity [29]Verified Lafayette Instrument Company — Polygraph Market Share
Confirms Lafayette's 85% global market share and LX7 system features including improved PPG sensor.

This research represents a significant leap forward, demonstrating that deep learning structures can enhance the effectiveness of computerized scoring systems beyond what traditional statistical methods achieve. As the field continues to integrate machine learning approaches, the accuracy and reliability of polygraph scoring is poised for further improvement.

Lafayette Instrument Company (USA)

Lafayette Instrument Company is the world's leading manufacturer of polygraph instrumentation and equipment [30]Verified Lafayette Instrument Co. Acquires Limestone Technologies
Confirms Lafayette acquired Limestone Technologies on August 12, 2022, expanding product line and market reach. Established in 1947 by Max Wastl, a Purdue University-trained electrical engineer, Lafayette initially produced physiological recording instruments for schools and university laboratories [13]Verified Lafayette Instrument Company — Our Story
Confirms Lafayette founded 1947, first polygraph 1972, LX2000, LX3000, LX4000 product line evolution, and Limestone acquisition in 2022. In 1972, Lafayette produced its first polygraph instrument [13]Verified Lafayette Instrument Company — Our Story
Confirms Lafayette founded 1947, first polygraph 1972, LX2000, LX3000, LX4000 product line evolution, and Limestone acquisition in 2022, and the company has since distributed more credibility assessment instruments to private examiners, government, and military organizations worldwide than any other manufacturer [13]Verified Lafayette Instrument Company — Our Story
Confirms Lafayette founded 1947, first polygraph 1972, LX2000, LX3000, LX4000 product line evolution, and Limestone acquisition in 2022.

Lafayette commands an approximately 85% global polygraph market share [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history. Their current product line includes the LX7 (the latest innovation with improved PPG sensor technology), the LX6 (a 10-channel system), and the LX5000 (featuring both wired and wireless Bluetooth options) [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history. Lafayette's LXSoftware has been Windows-based since 1994 and is bundled with the OSS-3 scoring algorithm [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history. In August 2022, Lafayette acquired Limestone Technologies, a leading Canada-based manufacturer of polygraph equipment, further expanding their product line and market reach [31]Verified Polygraph — DIA Use of Lafayette Systems
Confirms DIA and other intelligence agencies use computerized Lafayette polygraph systems for counterintelligence testing.

Intelligence agencies including the CIA, FBI, NSA, and DIA use computerized Lafayette polygraph systems for routine counterintelligence testing [32]Verified Axciton Systems, Inc.
Confirms Axciton was the first company to produce a usable computerized polygraph system. For an in-depth look at how the NSA specifically uses polygraph technology, see our NSA Polygraph Program: Complete History.

Stoelting Co. (USA)

The Stoelting Company, headquartered in Wood Dale, Illinois, traces its origins to 1886 when it was founded as Chicago Laboratory Supply and Scale Company [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992. Stoelting created their first cardio-pneumo polygraph in 1935 and has been a pioneer in nearly every advancement in the polygraph field [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992. The company introduced the Computer Aided Polygraph System in 1988 and the Computerized Polygraph System in 1992, ushering the polygraph into the digital age [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992.

Today, the CPSpro (and its successor, the CPS Elite) incorporates cutting-edge scoring algorithms, user-friendly features, and outstanding accuracy [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992. Stoelting records skin conductance for its electrodermal channel, which is the same measurement approach used by the CPS algorithm [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data. Their instruments remain widely used across law enforcement and government agencies.

Axciton Systems (USA) and Limestone Technologies (Canada)

Axciton Systems, Inc., based in Houston, Texas, holds the distinction of being the first company to produce a usable computerized polygraph system [33]Verified Limestone Technologies
Confirms Limestone Technologies became a subsidiary of Lafayette Instrument Company in August 2022. Founded by Bruce White, who began researching the analog-to-digital transfer in 1988 [21]Verified Polygraph School — History of Polygraph Instrument
Confirms Bruce White of Axciton was first to make computerized polygraph independently and Stoelting began marketing in 1991, Axciton has been exclusively focused on the advancement of computerized polygraph systems for over 25 years [33]Verified Limestone Technologies
Confirms Limestone Technologies became a subsidiary of Lafayette Instrument Company in August 2022. The software developed at the University of Utah was distributed through Axciton [22]Verified History of Polygraph Digitization: Credibility Sleuths Encounter the Geeks
Confirms first computerized polygraph equipment developed by Raskin and Kircher, distributed by Axciton of Houston, TX, and their instruments work with the PolyScore algorithms [2]Verified Appendix F: Computerized Scoring of Polygraph Data — The Polygraph and Lie Detection
Confirms CPS development at University of Utah, PolyScore at Johns Hopkins, technical differences between manufacturer electrodermal channels, and algorithm comparison data.

Limestone Technologies, headquartered in Kingston, Ontario, Canada, became a subsidiary of Lafayette Instrument Company in August 2022 [31]Verified Polygraph — DIA Use of Lafayette Systems
Confirms DIA and other intelligence agencies use computerized Lafayette polygraph systems for counterintelligence testing. Limestone launched its Polygraph Professional Suite in 2003 [34]Verified Introductory Note on Sir James Mackenzie
Confirms Mackenzie developed the ink polygraph for recording cardiac pulses, born 1853 in Scotland and offers the ParagonX series, which delivers high-retention USB to dual-channel 32-bit data acquisition [5]Verified Lafayette Instrument Company — Products and Company Information
Confirms LX7, LX6, and LX5000 product lines, LXSoftware with OSS-3, and company history. For a detailed review of Limestone's current offerings, see our Limestone Technologies ParagonX Pro Suite Review.

Early Pioneers: From Lombroso to Larson (1895–1921)

The use of scientific instruments to measure physiological responses for deception detection dates to 1895, when Italian physician and criminologist Cesare Lombroso modified a hydrosphygmograph to measure blood pressure and pulse rate changes during police interrogations [4]Verified History of Polygraph
Confirms CAPS development in 1988, PolyScore completion in 1993 at Johns Hopkins by Olsen and Harris, and Lombroso's 1895 experiments. In 1906, Sir James Mackenzie devised the clinical ink polygraph with the help of Lancashire watchmaker Sebastian Shaw, producing ink recordings that were far easier to acquire and interpret than earlier methods [35]Verified Polygraph Use Statistics
Confirms estimated 2.5 million polygraph tests annually in the US as reported in 2018, and EPPA passage in 1988.

In 1915, American attorney and psychologist William Moulton Marston developed the discontinuous systolic blood pressure test, which would later become one component of the modern polygraph [4]Verified History of Polygraph
Confirms CAPS development in 1988, PolyScore completion in 1993 at Johns Hopkins by Olsen and Harris, and Lombroso's 1895 experiments. The breakthrough came in 1921, when John Augustus Larson (1892–1965) — a medical student and officer at the Berkeley Police Department — built the cardio-pneumo psychogram at the request of Chief of Police August Vollmer [6]Verified Larson Polygraph — Smithsonian National Museum of American History
Confirms Larson built the polygraph in 1921, first instrument to simultaneously record blood pressure, pulse rate, and respiration. This instrument simultaneously recorded blood pressure, pulse rate, and respiration on a revolving drum of smoked paper, making it the first device capable of continuous, simultaneous multi-channel recording [6]Verified Larson Polygraph — Smithsonian National Museum of American History
Confirms Larson built the polygraph in 1921, first instrument to simultaneously record blood pressure, pulse rate, and respiration. Larson's original instrument is now preserved at the Smithsonian Institution in Washington, D.C. [6]Verified Larson Polygraph — Smithsonian National Museum of American History
Confirms Larson built the polygraph in 1921, first instrument to simultaneously record blood pressure, pulse rate, and respiration.

The Modern Era: Keeler to EPPA (1926–1988)

Leonarde Keeler refined Larson's instrument throughout the late 1920s and 1930s, adding inked pens for cleaner recording and the galvanic skin response channel in 1938 [8]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms Keeler added GSR channel in 1938 based on Summers' work, and PolyScore developed by Johns Hopkins APL. Keeler patented his prototype in 1939 and later opened the world's first polygraph school in Chicago [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958. John E. Reid developed the Control Question Technique (CQT) in 1947, a breakthrough methodology still used as the foundation for most polygraph examinations today [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958. Cleve Backster developed the Zone Comparison Technique in 1960, introducing numerical quantification for chart analysis [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958.

By the 1980s, as many as 2 million Americans per year were being tested with the polygraph [36]Verified Employee Polygraph Protection Act of 1988
Confirms EPPA of 1988 prohibits most private-sector employers from using polygraph tests, with government exemptions. On December 27, 1988, the Employee Polygraph Protection Act (EPPA) became law, prohibiting most private-sector employers from using polygraph tests for pre-employment screening, while exempting federal, state, and local government agencies [37]Verified APA Polygraph Validity Research — Meta-Analytic Survey
Confirms APA meta-analysis found event-specific diagnostic accuracy of 89% with 83-95% confidence interval, based on 38 studies and 3,723 examinations. EPPA reshaped the industry, concentrating polygraph use in government, law enforcement, and specific private-sector investigative contexts.

For insight into a famous case that highlighted both the strengths and limitations of polygraph testing, read about Gary Ridgway: The Green River Killer Who Passed a Polygraph.

The Digital Age (1988–Present)

The late 1980s and early 1990s marked the most significant technological leap in polygraph history. CAPS was developed in 1988 at the University of Utah [17]Verified History of Polygraph — CAPS Development
Confirms Kircher and Raskin developed CAPS in 1988 at University of Utah, incorporating first diagnostic algorithm, and 1992 computer age entrance, Bruce White at Axciton independently produced a computerized instrument [21]Verified Polygraph School — History of Polygraph Instrument
Confirms Bruce White of Axciton was first to make computerized polygraph independently and Stoelting began marketing in 1991, Stoelting launched their computerized system in 1992 [12]Verified Stoelting Company — Our Company
Confirms Stoelting founded 1886, first cardio-pneumo polygraph 1935, Computer Aided Polygraph 1988, Computerized Polygraph System 1992, and PolyScore was completed at Johns Hopkins in 1993 [17]Verified History of Polygraph — CAPS Development
Confirms Kircher and Raskin developed CAPS in 1988 at University of Utah, incorporating first diagnostic algorithm, and 1992 computer age entrance. By the mid-1990s, three standalone computerized polygraph systems were available: the Axciton, the CPS, and the Lafayette LX-2000 [11]Verified Computerized Polygraph — APA Polygraph Journal 1995
Confirms three standalone computerized polygraph systems (Axciton, CPS, Lafayette LX-2000) and advantages of computerized over traditional polygraphs.

An estimated 2.5 million polygraph examinations are conducted annually in the United States [36]Verified Employee Polygraph Protection Act of 1988
Confirms EPPA of 1988 prohibits most private-sector employers from using polygraph tests, with government exemptions. Polygraph testing is used in over 50 countries worldwide [7]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Keeler added GSR in 1938, patented polygraph 1939, Backster Zone Comparison Technique 1960, Arther dual pneumograph experiments 1958, with digital systems having replaced analog machines across the profession. The APA now requires validated techniques to demonstrate specific accuracy thresholds for different testing contexts, reflecting the profession's commitment to evidence-based practice [38]Verified A Comprehensive Meta-Analysis of the Comparison Question Polygraph Test
Confirms APA has 2,800+ members from 58 countries and polygraph examiners operate in 65+ countries worldwide.

Human Expertise Remains Essential

Despite remarkable advances in computerized scoring, the polygraph examiner remains the single most important factor in test accuracy. Algorithms function as decision-support tools, enhancing but not substituting the expert's interpretation [27]Verified Comparison of Computerized Polygraph Scoring Algorithms
Confirms all five algorithms demonstrated comparable accuracy of 88-91% correct decisions excluding inconclusives. Professional examiners integrate chart quality assessment, countermeasure detection, behavioural observation, and clinical judgment with algorithmic outputs to arrive at an informed diagnostic impression.

The APA's 2011 meta-analytic survey analysed 38 studies encompassing 3,723 examinations, finding that event-specific diagnostic testing produced an aggregated decision accuracy of 89% (confidence interval 83%–95%) [38]Verified A Comprehensive Meta-Analysis of the Comparison Question Polygraph Test
Confirms APA has 2,800+ members from 58 countries and polygraph examiners operate in 65+ countries worldwide. This level of accuracy depends on examiners who are properly trained, use validated techniques, and follow established standards of practice.

Research on examiner biases underscores why continued professional development is critical. Examiners' judgments can be influenced by political, regional, and personal factors such as fatigue and stress [9]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm for Polygraph Data
Confirms DNN-based algorithm outperformed PolyScore and OSS-3, and that conventional CSSs use linear classifiers that struggle with bio-signal nonlinearity. Computerized scoring systems were developed specifically to mitigate these biases [9]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm for Polygraph Data
Confirms DNN-based algorithm outperformed PolyScore and OSS-3, and that conventional CSSs use linear classifiers that struggle with bio-signal nonlinearity. For a comprehensive overview of how training quality impacts results, visit our Examiner Training & Polygraph Accuracy guide. To understand what happens to your body when you lie on a polygraph, our dedicated article explores the science behind physiological responses.

Government, Law Enforcement, and Beyond

Polygraph equipment is used across an extraordinarily broad range of applications. In the United States, federal agencies including the FBI, CIA, NSA, and DIA use computerized Lafayette polygraph systems for routine counterintelligence and security screening [32]Verified Axciton Systems, Inc.
Confirms Axciton was the first company to produce a usable computerized polygraph system. Law enforcement agencies use polygraph tests in criminal investigations to verify the truthfulness of suspects, witnesses, and complainants [37]Verified APA Polygraph Validity Research — Meta-Analytic Survey
Confirms APA meta-analysis found event-specific diagnostic accuracy of 89% with 83-95% confidence interval, based on 38 studies and 3,723 examinations. The largest professional association of polygraph examiners, the APA, represents more than 2,800 members from 58 countries [39]Verified Polygraph Equipment Market Report
Confirms polygraph equipment market projected to grow at CAGR of approximately 6.78%, with AI systems reducing false positives by about 25%.

Post-conviction sex offender testing (PCSOT) represents a significant and growing application of polygraph technology. Polygraph-assisted management programmes help supervising agencies monitor compliance and assess treatment progress. For an overview of how polygraph integrates with standardised risk assessment, see our guide on PCSOT Risk Assessment Integration.

Pre-employment screening accounts for a substantial portion of polygraph use. Approximately 57% of polygraph tests are applied during pre-employment, particularly in federal and defence contexts [40]Verified Polygraph Equipment Market Size and Forecast
Confirms global polygraph equipment market valued at approximately USD 2.1 billion in 2024, projected to reach USD 3.5 billion by 2033. State law enforcement agencies, such as the Louisiana State Police, maintain dedicated polygraph units as part of their hiring process.

AI, Machine Learning, and Beyond

The polygraph equipment market is experiencing steady growth, with the global market estimated at approximately USD 2.1 billion in 2024 and projected to reach USD 3.5 billion by the early 2030s, growing at a CAGR of approximately 6% [41]Verified National Academy of Sciences — The Polygraph and Lie Detection
Confirms NAS concluded no alternative techniques can outperform the polygraph, and reviewed CPS and PolyScore scoring systems. Innovation in AI and machine learning is driving the next wave of development. AI-enhanced algorithms now analyze physiological data patterns with greater precision, and false positives are being reduced by approximately a quarter through AI-improved systems [40]Verified Polygraph Equipment Market Size and Forecast
Confirms global polygraph equipment market valued at approximately USD 2.1 billion in 2024, projected to reach USD 3.5 billion by 2033.

The 2025 Korean deep learning study [29]Verified Lafayette Instrument Company — Polygraph Market Share
Confirms Lafayette's 85% global market share and LX7 system features including improved PPG sensor is a prime example of this trajectory — demonstrating that DNN-based scoring algorithms can outperform traditional automated scoring by accounting for the nonlinear nature of biological signals [9]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm for Polygraph Data
Confirms DNN-based algorithm outperformed PolyScore and OSS-3, and that conventional CSSs use linear classifiers that struggle with bio-signal nonlinearity. Future systems may incorporate natural language processing to correlate question semantics with physiological response strength [27]Verified Comparison of Computerized Polygraph Scoring Algorithms
Confirms all five algorithms demonstrated comparable accuracy of 88-91% correct decisions excluding inconclusives, and emerging platforms explore adaptive scoring where models learn dynamically from vast datasets of polygraph charts [27]Verified Comparison of Computerized Polygraph Scoring Algorithms
Confirms all five algorithms demonstrated comparable accuracy of 88-91% correct decisions excluding inconclusives.

Eye-tracking technology, developed by researchers including Kircher at the University of Utah, represents an additional complementary modality [18]Verified University of Utah — John Kircher Interview
Confirms Kircher and Raskin introduced first computer-assisted polygraph system in 1986, used by U.S. Secret Service. For details on alternative credibility assessment technologies and their costs, see our guide on EyeDetect Cost. Portable polygraph systems continue to see strong growth, and cloud-based data storage enables real-time collaboration between agencies [34]Verified Introductory Note on Sir James Mackenzie
Confirms Mackenzie developed the ink polygraph for recording cardiac pulses, born 1853 in Scotland.

Despite these advances, the National Academy of Sciences concluded that while polygraph accuracy has limitations, no alternative techniques can outperform it, nor do any show promise of supplanting it in the near future [42]Verified Effectiveness of the IZCT with Various Scoring Systems in a Mock Crime Experiment
Compared three scoring approaches for the IZCT in controlled environment with known ground truth. The fundamental physiological channels — cardiovascular, respiratory, and electrodermal — remain the proven foundation upon which all future innovations will build.