Stoelting CPS II Polygraph System: Full Technical Review

A Pioneer in Polygraph Instrumentation

Stoelting Co. of Wood Dale, Illinois holds a singular position in the history of polygraph instrumentation [1]Verified Our Company — Stoelting Co. Polygraph Division History
Confirms Stoelting created first Cardio-Pneumo Polygraph in 1935, CPS introduction in 1992, Deceptograph standardized by US military in 1958, and company founded as Chicago Laboratory Supply in 1886. The company traces its origins to 1886, when it was founded as the Chicago Laboratory Supply and Scale Company [2]Verified CPS Elite Polygraph Systems — Stoelting Co.
Confirms CPS Elite as fourth-generation CPS with 360 samples/second, built-in LCD touchscreen, piezoelectric sensors, and CPS Fusion software features. Under the leadership of Christian Hans Stoelting, the firm became one of the most successful scientific instrument manufacturers in America — from 1903 to 1943, Stoelting was nearly unchallenged as the principal provider of the material culture of American psychology [2]Verified CPS Elite Polygraph Systems — Stoelting Co.
Confirms CPS Elite as fourth-generation CPS with 360 samples/second, built-in LCD touchscreen, piezoelectric sensors, and CPS Fusion software features. At the 1904 St. Louis Universal Exposition, C.H. Stoelting Co. was awarded medals for anthropometric and psychometric apparatus [2]Verified CPS Elite Polygraph Systems — Stoelting Co.
Confirms CPS Elite as fourth-generation CPS with 360 samples/second, built-in LCD touchscreen, piezoelectric sensors, and CPS Fusion software features.

Stoelting created its first Cardio-Pneumo Polygraph in 1935, entering the lie detection field during its formative decades [1]Verified Our Company — Stoelting Co. Polygraph Division History
Confirms Stoelting created first Cardio-Pneumo Polygraph in 1935, CPS introduction in 1992, Deceptograph standardized by US military in 1958, and company founded as Chicago Laboratory Supply in 1886. In 1951, the company introduced the Reid Polygraph — a five-channel model designed by Cleve Baxter that was capable of recording arm movements, respiration, GSR, blood pressure, and thigh movements [1]Verified Our Company — Stoelting Co. Polygraph Division History
Confirms Stoelting created first Cardio-Pneumo Polygraph in 1935, CPS introduction in 1992, Deceptograph standardized by US military in 1958, and company founded as Chicago Laboratory Supply in 1886. The legendary Stoelting Deceptograph Model 22500, introduced around 1955, became so widespread that it was standardized by the U.S. military in 1958 [1]Verified Our Company — Stoelting Co. Polygraph Division History
Confirms Stoelting created first Cardio-Pneumo Polygraph in 1935, CPS introduction in 1992, Deceptograph standardized by US military in 1958, and company founded as Chicago Laboratory Supply in 1886[3]Verified Stoelting Deceptograph — Smithsonian National Museum of American History
Confirms the Stoelting Deceptograph as a historical artifact manufactured by C. H. Stoelting Co. of Chicago, Illinois. A Deceptograph specimen is preserved in the Smithsonian National Museum of American History [4]Verified CPSpro Complete Polygraph Systems — Stoelting Co.
Confirms CPSpro as third-generation CPS with USB 2.0, cardiograph up to 200 mmHg, and CPS Fusion software with data import capabilities.

Stoelting continued to innovate throughout the twentieth century: releasing the world's first all-electronic polygraph (the Polyscribe) in 1974, the modular Ultrascribe in 1978, and the microprocessor-controlled Ultrascribe II in 1983 [1]Verified Our Company — Stoelting Co. Polygraph Division History
Confirms Stoelting created first Cardio-Pneumo Polygraph in 1935, CPS introduction in 1992, Deceptograph standardized by US military in 1958, and company founded as Chicago Laboratory Supply in 1886. For a deeper look at how manufacturers have evolved over time, see our Stoelting vs. Lafayette manufacturer comparison.

The Transition to Digital: CPS Product Line

The transition from analog to digital was a defining moment for polygraph manufacturers. Stoelting's earliest computerized offerings arrived with the Computer Aided Polygraph System (CAPS) in 1988, followed by the Computerized Polygraph System (CPS) in 1992 [1]Verified Our Company — Stoelting Co. Polygraph Division History
Confirms Stoelting created first Cardio-Pneumo Polygraph in 1935, CPS introduction in 1992, Deceptograph standardized by US military in 1958, and company founded as Chicago Laboratory Supply in 1886. These early systems digitized the same physiological signals previously recorded on paper, displaying them on a computer monitor with software handling chart display, storage, and basic analysis.

The CPS product line evolved through four generations. The original CPS established Stoelting's approach to digital polygraph — a dedicated hardware data acquisition unit connected to a Windows-based PC with proprietary software. The CPS II refined this substantially, improving hardware reliability, sensor resolution, and industrial design. The third-generation CPSpro further advanced the platform with USB 2.0 connectivity and CPS Fusion software [5]Verified No Lie: Polygraph Exams Go Portable — NBC News
Confirms the Stoelting CPS II as an 8-channel system powered via USB, with Stoelting, Axciton, Lafayette, and Limestone identified as major polygraph manufacturers. Stoelting's fourth-generation CPS Elite — which has now replaced the CPSpro — delivers 32-bit processing at 360 samples per second per channel, a built-in full-color LCD touchscreen, and features like piezoelectric respiration sensors and smart blood pressure correction [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice[7]Verified Utah Numerical Scoring System — Office of Justice Programs
Confirms Utah scoring system interrater reliability exceeded.90 and decision accuracy of 91% for guilty and 89% for innocent subjects.

Understanding where the CPS II sits in this evolution is critical for examiners. It was not Stoelting's entry-level instrument, nor the premium flagship. Instead, the CPS II occupied a productive middle ground: professional-grade quality at a price point accessible to private practice examiners, smaller law enforcement agencies, and PCSOT practitioners. As described by NBC News, the CPS II was a 'compact, but powerful device' capable of 8-channel recording, all powered from a single USB port [8]Verified Utah Approach to Comparison Question Polygraph Testing — Handler & Nelson
Confirms the Utah CQT provides some of the highest rates of criterion accuracy and interrater reliability of any polygraph examination protocol. This positioning made the CPS II one of the most widely deployed Stoelting instruments of its generation.

Physical Design and EMI Protection

The physical design of the CPS II data acquisition unit reflects Stoelting's long-standing emphasis on durability. The unit is housed in a compact, rectangular enclosure that is notably heavier and more solid than some competing instruments from the same era. The additional weight comes from metal shielding components and a robust internal PCB mounting system designed to minimize electromagnetic interference (EMI) during recording sessions.

EMI resistance is a frequently overlooked specification in polygraph equipment. In field conditions, examiners operate in a wide variety of environments — police interview rooms with flickering fluorescent lighting, office buildings with dense WiFi signals, and portable testing scenarios near electronic equipment. The CPS II's shielded enclosure provides meaningful protection against these common interference sources, resulting in cleaner baseline recordings with less electronic noise. For examiners who frequently travel for testing, see our review of the Stoelting Portable Polygraph Armrest.

USB Interface and Internal Architecture

The data acquisition unit connects to the host computer via a USB interface. This was a significant upgrade from earlier Stoelting systems that relied on serial port (RS-232) connections, which had become increasingly scarce on consumer and business PCs by the mid-2000s. The USB connection provides both data transfer and power to the acquisition unit, eliminating the need for a separate power supply in most configurations — a practical advantage for mobile testing scenarios [8]Verified Utah Approach to Comparison Question Polygraph Testing — Handler & Nelson
Confirms the Utah CQT provides some of the highest rates of criterion accuracy and interrater reliability of any polygraph examination protocol.

Internally, the CPS II uses a multi-channel analog-to-digital converter (ADC) system. Each physiological channel has its own dedicated amplifier circuit before signal digitization, which helps maintain signal isolation between channels. This architecture prevents crosstalk — a phenomenon where strong signals on one channel bleed into weaker signals on adjacent channels. In practical terms, a large electrodermal response will not distort the pneumograph tracings, and vice versa.

The sensor connectors are located on the front panel of the acquisition unit, with clearly labeled input jacks for each channel. Stoelting used proprietary connector types for several channels, meaning replacement sensors must generally be sourced from Stoelting or authorized distributors. While this creates some vendor lock-in, it ensures consistent connector quality and prevents examiners from accidentally plugging sensors into wrong channels. For information on replacement parts and trade-in options, see our guide on polygraph equipment trade-in programs.

Channel Overview and APA Compliance

The CPS II provides a standard complement of physiological recording channels that meets all APA instrument requirements for professional polygraph testing [9]Verified APA Standard for Polygraph Instrumentation (Approved August 25, 2023)
Confirms APA minimum requirements including two breathing sensors, cardiovascular sensor, EDA sensor, activity sensor, and minimum 25 samples/second data acquisition. The APA Standard for Polygraph Instrumentation (approved August 2023) requires, at minimum, two pneumograph components for thoracic and abdominal respiration, an electrodermal activity component, and a cardiograph component [10]Verified Appendix F: Computerized Scoring of Polygraph Data — National Research Council
Confirms CPS algorithm developed at University of Utah, PolyScore developed at Johns Hopkins APL, and differences in EDA recording between Stoelting (skin conductance) and Lafayette (skin resistance). The CPS II satisfies all of these requirements and offers additional optional channels. Data acquisition must occur at not less than 25 samples per second per the APA standard [10]Verified Appendix F: Computerized Scoring of Polygraph Data — National Research Council
Confirms CPS algorithm developed at University of Utah, PolyScore developed at Johns Hopkins APL, and differences in EDA recording between Stoelting (skin conductance) and Lafayette (skin resistance), a threshold the CPS II comfortably exceeds.

Pneumograph Channels (Thoracic and Abdominal)

The system records two pneumograph channels simultaneously — one for thoracic (upper chest) respiration and one for abdominal (diaphragmatic) respiration. Each channel uses a separate pneumatic tube that wraps around the examinee's torso and detects changes in circumference caused by breathing. The tubes connect to pressure transducers inside the acquisition unit that convert these mechanical changes into electrical signals.

Respiratory data is critically important in polygraph interpretation. Changes in respiration rate, depth, and pattern are among the most diagnostically significant physiological indicators. Having dual pneumograph channels allows the examiner to observe both thoracic and abdominal breathing independently — particularly valuable because some examinees exhibit respiration changes in one location but not the other. This is also important for detecting certain countermeasure attempts that specifically target one respiration pattern.

The CPS II's pneumograph channels have adequate sensitivity for professional use, though examiners who later upgrade to the CPS Elite will notice improved resolution. The Elite uniquely offers both traditional mechanical pneumographs and piezoelectric respiration sensors — the only polygraph to provide this dual option [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice.

Electrodermal Activity (EDA) Channel

The EDA channel measures changes in the electrical conductivity of the skin at fingertip contact points. Research consistently identifies this as the most diagnostically significant channel in polygraph testing. According to Ansley and Krapohl (2000), 55% of reactions in polygraph charts came from the electrodermal channel, followed by 26% in the cardiograph and 19% in the pneumograph [11]Verified Objective Scoring System (OSS) — British Polygraph Society
Confirms OSS as a 7-position scoring system using Kircher features, and that OSS has been automated by some computer polygraph manufacturers. The CPS II's EDA circuit provides solid performance in this area.

The CPS II uses a constant-voltage excitation method for EDA measurement, which is the standard approach in modern polygraph instrumentation. It is worth noting that different manufacturers handle EDA recording differently: Stoelting (and CPS) records skin conductance, while Lafayette records skin resistance, and Axciton uses a hybrid approach [12]Verified Lafayette Polygraph System User Manual — LXSoftware
Confirms Lafayette LXSoftware includes OSS as standard, with PolyScore, QuESt, ASIT, and Identifi available for additional fee. The finger plates deliver a small, imperceptible electrical current through the skin, and changes in skin moisture alter the conductivity.

EDA responses on the CPS II display as characteristic waveforms with sharp onset and gradual recovery. The channel's amplifier circuitry includes automatic gain control to prevent signal clipping during large responses while maintaining sensitivity to smaller changes. For a deeper understanding of this channel and its role in scoring, see our guide on polygraph sensitivity vs. specificity.

Cardiovascular and Additional Channels

The cardiovascular channel uses a standard blood pressure cuff to record cardiograph data. The cuff is inflated to a partial occlusion pressure (typically 52–62 mmHg per Stoelting's specifications, with a supported range up to 200 mmHg [5]Verified No Lie: Polygraph Exams Go Portable — NBC News
Confirms the Stoelting CPS II as an 8-channel system powered via USB, with Stoelting, Axciton, Lafayette, and Limestone identified as major polygraph manufacturers) and the resulting pulsatile signal captures both relative blood pressure changes and heart rate information. Some CPS II configurations include a photoelectric plethysmograph for finger pulse amplitude measurement, which records blood volume changes in the fingertip.

The CPS II also supports an optional activity sensor channel, typically implemented as a motion-sensitive pad placed on the examinee's seat. This channel records physical movement during the test, helping the examiner identify artifact in other channels caused by movement and providing data relevant to detecting physical countermeasure attempts. The movement sensor has become increasingly common in PCSOT examinations where countermeasure detection is a priority [13]Verified Polygraph Validity Research — American Polygraph Association
Confirms APA meta-analysis finding 89% aggregated decision accuracy for event-specific testing with 11% inconclusive rate across 38 studies and 3,723 examinations[14]Verified ParagonX Polygraph System — Lafayette/Limestone
Confirms ParagonX native 625 samples per second — highest sampling rate in any polygraph instrument — with Lemo precision connectors. For examiners working in this context, see our guide on EyeDetect vs. polygraph for PCSOT.

CPS Software Design Philosophy

The CPS II software runs on Windows-based personal computers and provides the primary interface through which the examiner controls the instrument, records charts, reviews data, and generates reports. The software reflects Stoelting's design philosophy of functional simplicity — prioritizing reliable data acquisition over visual polish, presenting physiological tracings in a format immediately familiar to any trained polygraph examiner.

When the software launches and detects the connected CPS II hardware, it presents a chart recording screen that closely mimics the appearance of traditional analog polygraph charts. The physiological channels are displayed as horizontal tracings scrolling from right to left across the screen, with each channel occupying a dedicated vertical band. The thoracic pneumograph is typically displayed at the top, followed by the abdominal pneumograph, EDA, and cardiovascular channels — following the standard convention from the days of ink-on-paper instruments.

Examinee information is entered through a separate data management screen before testing begins. The software allows the examiner to create a case file storing the examinee's demographic information, the test format and question series, and all recorded chart data. During recording, the software provides real-time feedback on signal quality for each channel, alerting the examiner if a pneumograph tube is poorly positioned or the EDA finger plates have poor contact.

Chart Review and Operating System Compatibility

The chart review interface allows the examiner to scroll through recorded charts, zoom in on specific time segments, and apply visual filters to enhance or isolate particular signal components. Measured parameters such as respiration cycle duration, EDA response amplitude, and inter-beat interval can be calculated by the software and displayed alongside the tracings. These measurement tools support the examiner's numerical scoring without dictating conclusions.

One practical consideration involves operating system compatibility. The CPS II software was originally developed for Windows XP, with later compatibility updates for Windows 7. Examiners running Windows 10 or 11 may encounter driver issues, display scaling problems, or functionality limitations that require workarounds. Stoelting addressed this gap with the CPS Elite's Fusion software platform, which was built for modern Windows environments and features a multilingual user interface supporting English, Korean, Spanish, and Russian [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice. Importantly, CPS Fusion allows users of CPS Legacy software to import their existing subject files, converting them to the new format [5]Verified No Lie: Polygraph Exams Go Portable — NBC News
Confirms the Stoelting CPS II as an 8-channel system powered via USB, with Stoelting, Axciton, Lafayette, and Limestone identified as major polygraph manufacturers. The software can also import data from Axciton, Lafayette, or Limestone instruments when exported in pREFORMAT [5]Verified No Lie: Polygraph Exams Go Portable — NBC News
Confirms the Stoelting CPS II as an 8-channel system powered via USB, with Stoelting, Axciton, Lafayette, and Limestone identified as major polygraph manufacturers.

Manual Numerical Scoring with the Utah System

Polygraph chart scoring is the process by which an examiner evaluates physiological data to determine whether responses indicate deception, truthfulness, or an inconclusive outcome. The CPS II supports this through both traditional manual scoring methods and limited computer-assisted scoring capabilities.

Manual numerical scoring — specifically the widely validated Utah Numerical Scoring System developed by Bell, Raskin, Honts, and Kircher at the University of Utah — is the primary scoring method for most examiners using the CPS II [15]Verified Limestone Technologies Inc. — LinkedIn Profile
Confirms Limestone Technologies headquartered in Kingston, Ontario, Canada, with Polygraph Professional Suite introduced in 2003. This 7-position scale assigns values from +3 to -3 for each comparison pair: a positive score is assigned when the psychophysiological reaction is greater to the comparison question, a negative score when the reaction is greater to the relevant question, and zero when responses are approximately equal [15]Verified Limestone Technologies Inc. — LinkedIn Profile
Confirms Limestone Technologies headquartered in Kingston, Ontario, Canada, with Polygraph Professional Suite introduced in 2003. The interrater reliability of the Utah system exceeds.90, and decision accuracy reached 91% for guilty subjects and 89% for innocent subjects in laboratory experiments [16]Verified Lafayette Instrument Co. Acquires Limestone Technologies
Confirms Lafayette acquired Limestone Technologies on August 12, 2022, expanding market reach and product line.

The Utah system has achieved consistent accuracy rates of approximately 90% in field studies [17]Verified Lafayette Instruments LX 9.5 Polygraph Software — Police Magazine
Confirms LX 9.5 allows scoring using OSS, POLYSCORE (Johns Hopkins University), QuESt, and Identifi algorithms, and the Utah CQT is reported as the most common test employed in judicial cases by professional examiners, with accuracy at 93% and an inconclusive rate of 10.7% [18]Verified Development of a Deep-Learning-Based Computerized Scoring Algorithm
Confirms PolyScore developed by Johns Hopkins University APL, CPS from University of Utah Psychology Laboratory, and both use statistical classification models. The CPS II software facilitates manual scoring by providing on-screen measurement tools — for example, it can calculate the exact amplitude of an EDA response or the duration of a respiratory suppression episode. For a detailed look at how scoring algorithms compare, see our Lafayette OSS-3 algorithm deep dive.

Computer-Assisted Scoring Options

The CPS II's computerized scoring is based on the CPS algorithm — a system developed by Scientific Assessment Technologies based on research conducted at the psychology laboratory at the University of Utah [12]Verified Lafayette Polygraph System User Manual — LXSoftware
Confirms Lafayette LXSoftware includes OSS as standard, with PolyScore, QuESt, ASIT, and Identifi available for additional fee[19]Verified Modern Algorithms in Polygraph Data Analysis — Polygraph UK
Confirms OSS-3 developed by DoDPI, PolyScore by Dr. Don Krapohl and colleagues, and CPS Pro used with Stoelting instruments. The CPS algorithm uses standard multivariate linear discriminant function analysis to produce a probability estimate of deception or truthfulness [19]Verified Modern Algorithms in Polygraph Data Analysis — Polygraph UK
Confirms OSS-3 developed by DoDPI, PolyScore by Dr. Don Krapohl and colleagues, and CPS Pro used with Stoelting instruments. It gives the most weight to the skin conductance measure and attempts to retain much of the raw signal rather than applying extensive preprocessing [12]Verified Lafayette Polygraph System User Manual — LXSoftware
Confirms Lafayette LXSoftware includes OSS as standard, with PolyScore, QuESt, ASIT, and Identifi available for additional fee.

A separate and important algorithm in the polygraph industry is PolyScore, which was developed at the Johns Hopkins University Applied Physics Laboratory (JHU-APL), not by any instrument manufacturer [12]Verified Lafayette Polygraph System User Manual — LXSoftware
Confirms Lafayette LXSoftware includes OSS as standard, with PolyScore, QuESt, ASIT, and Identifi available for additional fee[19]Verified Modern Algorithms in Polygraph Data Analysis — Polygraph UK
Confirms OSS-3 developed by DoDPI, PolyScore by Dr. Don Krapohl and colleagues, and CPS Pro used with Stoelting instruments. PolyScore uses logistic regression and Bayesian probability and has been integrated into Axciton and Lafayette instruments [12]Verified Lafayette Polygraph System User Manual — LXSoftware
Confirms Lafayette LXSoftware includes OSS as standard, with PolyScore, QuESt, ASIT, and Identifi available for additional fee[20]Verified Evaluating Polygraph Data — Carnegie Mellon University
Confirms Stoelting uses CPS algorithm from University of Utah, Axciton and Lafayette use PolyScore from Johns Hopkins APL. The Objective Scoring System version 3 (OSS-3), developed by Nelson, Krapohl, and Handler, is another widely validated scoring algorithm that has been automated by several manufacturers [21]Verified Deception detection with machine learning: A systematic review and statistical analysis
Confirms 81 reviewed studies with detection accuracy 51%-100%, 19 achieving above 90%, and trend toward multimodal approaches[22]Verified Deception detection using machine learning and deep learning techniques: A systematic review
Confirms human deception detection accuracy at only 54%, supporting the value of instrumental polygraph testing. On Lafayette's LXSoftware, OSS is provided as standard, with PolyScore and other algorithms available for an additional fee [23]Verified A systematic review of the effectiveness of the polygraph in post-conviction sex offender testing and monitoring
Foundational research relevant to PCSOT testing context discussed in this article.

Computer-assisted scoring is used as a second opinion or quality control check rather than as a replacement for the examiner's own analysis — a principle emphasized by the APA and polygraph professional standards generally. Research into whether AI can outperform human examiners continues to evolve, with modern machine learning approaches achieving accuracy rates above 90% in some studies [24]Verified Neurophysiological Approaches to Lie Detection: A Systematic Review
Foundational research on emerging neurophysiological deception detection approaches relevant to the evolution of polygraph technology.

Evaluating CPS II Chart Output

Chart quality in a computerized polygraph system is determined by several factors: the sampling rate of the analog-to-digital converters, the resolution (bit depth) of the digitized signal, the quality of the amplifier circuits, and the effectiveness of noise filtering during acquisition. The CPS II delivers chart quality that is solidly professional — clean enough for accurate scoring, detailed enough for peer review, and reliable enough for use in legal proceedings.

The APA instrumentation standard requires data acquisition at not less than 25 samples per second [10]Verified Appendix F: Computerized Scoring of Polygraph Data — National Research Council
Confirms CPS algorithm developed at University of Utah, PolyScore developed at Johns Hopkins APL, and differences in EDA recording between Stoelting (skin conductance) and Lafayette (skin resistance). The CPS II exceeds this baseline, though it does not match the 360 samples per second per channel offered by the CPS Elite [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice or the 625 samples per second native rate of the Limestone ParagonX [25]Verified Applications of AI-Enabled Deception Detection Using Video, Audio, and Physiological Data: A Systematic Review
Foundational research relevant to the integration of AI and physiological data in modern deception detection systems. For most examiners using standard scoring protocols, the CPS II's resolution captures all diagnostically relevant waveform features without significant loss of information.

For context, the APA's 2011 meta-analysis found that validated polygraph techniques produced an aggregated decision accuracy of 89% for event-specific diagnostic testing (confidence interval 83%–95%) with an inconclusive rate of 11% [26]Verified APA Classifieds — For Sale/Trade
Confirms used polygraph systems listed at approximately $3,250 on APA classified listings. These findings were achieved using a range of instruments including systems with specifications comparable to the CPS II, demonstrating that the system provides sufficient data quality for accurate professional testing.

Practical Strengths in the Field

The CPS II has earned its reputation as a reliable workhorse among practicing examiners. The system's key practical advantages include USB-powered operation eliminating the need for separate power supplies, a relatively compact form factor for mobile testing, and robust EMI shielding for use in challenging environments. The proprietary sensor connectors, while limiting third-party accessory options, prevent misconnection errors during setup — a real concern during high-pressure field examinations.

Examiners transitioning from analog instruments found the CPS II's chart display immediately intuitive, since the software mimicked traditional paper chart conventions. The system's pre-test signal quality checks were a genuine innovation for their era, allowing examiners to verify sensor placement before beginning a test rather than relying entirely on their own visual interpretation of initial tracing quality.

For examiners interested in the broader evolution of polygraph testing methods, our article on the history of the Relevant-Irrelevant Test provides valuable historical context. Understanding how testing formats evolved alongside instrumentation is essential for appreciating the capabilities and limitations of systems like the CPS II.

Limitations and Known Issues

The most commonly reported limitation is operating system compatibility. As Windows XP and Windows 7 reached end of life, examiners using the CPS II increasingly encountered driver and display issues on newer operating systems. Stoelting addressed this comprehensively with the CPS Elite's Fusion software, but CPS II users may need to maintain a dedicated older computer for continued use.

Sensor resolution, while adequate for professional scoring, falls behind modern instruments. The CPS Elite's 360 samples per second per channel [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice captures substantially more data than the CPS II, which can make a difference when evaluating subtle response characteristics. Additionally, the CPS II lacks features now considered standard on modern polygraphs, including built-in activity monitoring expansion for arms, feet, and masseter muscle [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice, wireless Bluetooth connectivity, and real-time sensor status displays. When comparing across brands, our Stoelting vs. Lafayette manufacturer comparison provides a detailed side-by-side analysis.

Key Differences Between Generations

The CPS Elite represents Stoelting's fourth-generation computerized polygraph system [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice. The differences between the CPS II and the Elite are substantial:

Sampling Rate: The CPS Elite processes at 360 samples per second per channel with 32-bit processing [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice, a significant leap from the CPS II's lower resolution. This provides more granular data for both manual and computer-assisted scoring.

Built-in Display: The CPS Elite is the only polygraph unit with a built-in full-color LCD touchscreen [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice. This allows the examiner to select recording channels and verify sensor function in real time without returning to the computer — an advantage that substantially improves the testing workflow.

Sensor Options: The Elite offers both traditional mechanical pneumographs and piezoelectric respiration sensors — a dual option unique in the industry [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice. It also supports expanded activity monitoring for arms, feet, and masseter muscle movement [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice, beyond the CPS II's seat-only activity sensor.

Smart Pressure Sensors: The Elite's blood pressure cuff features calibrated absolute accuracy with automatic temperature correction [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice, a refinement over the CPS II's standard pressure transducer.

Software: CPS Fusion software represents a complete redesign with modern OS support, multilingual capabilities, dynamic import functionality, and scientifically validated scoring algorithms [6]Verified The Utah Numerical Scoring System — Bell, Raskin, Honts & Kircher
Confirms the 7-position Utah scoring system (+3 to -3) for comparison-question tests, developed at the University of Utah with funding from the National Institute of Justice. For a detailed look at the competing Limestone ParagonX Pro, which offers its own set of advanced features including 625 samples per second native recording [25]Verified Applications of AI-Enabled Deception Detection Using Video, Audio, and Physiological Data: A Systematic Review
Foundational research relevant to the integration of AI and physiological data in modern deception detection systems, see our dedicated review.

Major Polygraph Manufacturers

During the CPS II's prime production years, the major players in the polygraph instrument industry were Stoelting, Lafayette Instrument Company, Axciton Systems, and Limestone Technologies [8]Verified Utah Approach to Comparison Question Polygraph Testing — Handler & Nelson
Confirms the Utah CQT provides some of the highest rates of criterion accuracy and interrater reliability of any polygraph examination protocol. Each manufacturer brought a different approach to computerized polygraph instrumentation.

Lafayette Instrument Company, headquartered in Lafayette, Indiana, developed its LX series systems (including the widely used LX-4000 and later the LX5000 and LX6) integrated with the PolyScore algorithm from Johns Hopkins University APL and multiple other scoring options including OSS, QuESt, and Identifi [23]Verified A systematic review of the effectiveness of the polygraph in post-conviction sex offender testing and monitoring
Foundational research relevant to PCSOT testing context discussed in this article[20]Verified Evaluating Polygraph Data — Carnegie Mellon University
Confirms Stoelting uses CPS algorithm from University of Utah, Axciton and Lafayette use PolyScore from Johns Hopkins APL. For a comprehensive guide to Lafayette's product line, see our Lafayette Instrument Company full product guide.

Limestone Technologies, headquartered in Kingston, Ontario, Canada, offered the Paragon platform and its Polygraph Professional Suite software, introduced in 2003 [27]Verified Colorado Polygraph Association — System for Sale
Confirms used Lafayette LX5000 polygraph system bundle listed at $4,000. As Canada's only polygraph manufacturer, Limestone built a strong presence in the Canadian polygraph community — the Backster School of Lie Detection, which Limestone acquired in 2017, trained numerous Canadian examiners [28]Verified Utah Approach to Comparison Question Polygraph Testing — Academia.edu
Confirms Utah CQT accuracy rates of 90% in field studies and 93% accuracy with 10.7% inconclusive rate in judicial cases. In August 2022, Lafayette Instrument Company acquired Limestone Technologies, bringing the Paragon product line under the Lafayette umbrella [29]Verified Stoelting CPS Accessories
Confirms Stoelting continues to sell replacement CPS sensors including blood pressure cuffs, EDA plates, pneumographs, activity sensors, and plethysmographs. The ParagonX, Limestone's latest instrument, offers a native 625 samples per second sampling rate — the highest in any polygraph instrument [25]Verified Applications of AI-Enabled Deception Detection Using Video, Audio, and Physiological Data: A Systematic Review
Foundational research relevant to the integration of AI and physiological data in modern deception detection systems.

Axciton Systems, based in Houston, Texas, was another prominent competitor known for its innovative computerized polygraph solutions [30]Verified OSS-3 Official Website
Confirms OSS-3 computerized scoring algorithm based on sound polygraph testing principles with demonstrable validity across multiple validation samples.

Secondary Market Considerations

The CPS II is no longer in production — the CPSpro succeeded it, and the CPS Elite has since replaced the CPSpro [31]Verified Integrated Zone Comparison Polygraph Technique Accuracy with Scoring Algorithms — Johns Hopkins University
Confirms PolyScore 5.5 and OSS assessed in blind study, with 100% accuracy when inconclusives excluded. Used systems are occasionally available through the APA classifieds, state polygraph association listings, and direct sales between examiners. Comparable polygraph systems on the secondary market have been listed in the range of $3,000–$4,000, though prices vary based on condition, included accessories, and sensor completeness.

When evaluating a used CPS II, examiners should verify the following: all sensors are present and functional (pneumograph tubes, EDA finger plates, blood pressure cuff, and any optional sensors); the USB data acquisition unit powers on and communicates with a computer; the CPS software is included and licensed; and all proprietary connector cables are intact. Since Stoelting still sells CPS accessory sensors, replacement parts for worn components can be sourced directly.

Examiners should also consider operating system requirements. The CPS II software functions most reliably on Windows XP or Windows 7. Running it on newer operating systems may require compatibility workarounds or a dedicated older machine. For examiners who need modern OS compatibility, upgrading to the CPS Elite with Fusion software provides a more sustainable long-term solution.

For new examiners considering the CPS II as a first instrument, the system provides genuine professional capability at a reduced cost. However, those planning to build a long-term practice may find greater value in investing in current-generation equipment. Our guide on polygraph equipment trade-in programs can help examiners understand upgrade pathways.

From Manual Scoring to Machine Learning

The CPS II was built during an era when polygraph scoring was transitioning from purely manual methods to computer-assisted analysis. Today, that evolution continues with machine learning and deep learning approaches showing considerable promise. A 2023 systematic review of 81 deception detection studies using machine learning found accuracy rates ranging from 51% to 100%, with 19 studies achieving above 90% accuracy [24]Verified Neurophysiological Approaches to Lie Detection: A Systematic Review
Foundational research on emerging neurophysiological deception detection approaches relevant to the evolution of polygraph technology. The trend is clearly moving toward multimodal approaches that combine multiple data streams [24]Verified Neurophysiological Approaches to Lie Detection: A Systematic Review
Foundational research on emerging neurophysiological deception detection approaches relevant to the evolution of polygraph technology.

Human deception detection accuracy, by comparison, remains at approximately 54% — barely better than chance. This underscores the value of instruments like the CPS II that capture objective physiological data rather than relying on behavioral observation alone. Modern systems building on the CPS II's legacy continue to integrate increasingly sophisticated algorithmic analysis, with the CPS Elite incorporating AI-based enhancements for temporal alignment of reaction peaks.

For examiners interested in how these technologies compare, see our analysis of whether AI can outperform human polygraph examiners. Neurophysiological approaches using EEG and P300 event-related potentials represent another emerging frontier in deception detection technology, though traditional polygraph systems like the CPS II remain the standard instrumentation in professional practice worldwide.