Calibration vs Verification in ISO/IEC 17025: A Laboratory Manager's Guide

Calibration in the ISO/IEC 17025 sense is a measurement activity that links an instrument’s readings to known reference standards. The formal definition (from the VIM, which ISO 17025 adopts) is: an operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication. In simpler terms, calibration means comparing the instrument or device (often called the Unit Under Calibration, UUC) against a higher-accuracy reference standard to determine the UUC’s measurement error and uncertainty. This process tells you how far off the instrument’s readings are from the true values. For example, if you calibrate a thermometer, you measure its reading at known true temperatures and find the deviation (error) at each point.

During calibration, the laboratory uses traceable standards – i.e. reference instruments or materials that have themselves been calibrated to higher standards – to ensure an unbroken chain of comparisons back to SI units​. The result of a calibration is typically a set of data: the UUC’s indicated values versus the true values from the standard, along with the measurement uncertainties of those values. Calibration does not inherently adjust or fix the instrument; it is essentially a characterization of the instrument’s accuracy. After calibration, one might adjust the instrument to correct its performance, but adjustment is a separate step following calibration (and not part of the calibration definition). Likewise, calibration by itself does not tell you if the instrument meets any specific tolerance or specification – it simply provides the measured error. Determining compliance with specs is actually the role of verification (or a decision by the user based on calibration data).

Key points about calibration:

• Purpose: To determine the measurement accuracy of equipment and establish traceability. Calibration quantifies how far the instrument’s readings deviate from true values and estimates the uncertainty in those readings. It ensures your measurements are anchored to national or international standards (e.g. via NIST, BIPM) so that results are trustworthy and comparable​.
• Process: Involves a comparison of the UUC against a known standard under controlled conditions. The technician follows a defined procedure, measures the UUC at one or more points, and records the differences from the standard. For instance, to calibrate a scale, you would place certified weights on it and record the indicated weight vs. the true weight. Multiple points are checked across the instrument’s range as needed. Environmental conditions (temperature, humidity, etc.) may be controlled or noted, since calibration conditions can affect results. Critically, the measurement uncertainty of the results is calculated or at least accounted for – this quantifies the confidence in the measurement data. Without an uncertainty analysis and traceability, one cannot truly call the process a calibration; it would just be a simple check. In fact, ISO 17025 and metrology standards insist that calibration includes estimating uncertainty and ensuring traceable references; without these two, we cannot call it calibration; we are just performing a simple verification.
• Traceability: Every calibration must be tied to recognized standards. This means the reference instrument or artifact used has a calibration certificate linking it to higher standards, ultimately to SI units. ISO/IEC 17025:2017 emphasizes metrological traceability as an essential aspect of calibration activities (Clause 6.5)​. Thanks to traceability, a calibrated thermometer in your lab can be related back to the International Temperature Scale, for example. This unbroken chain of comparisons is what gives calibration its credibility.
• Documentation: The outcome of a calibration is documented in a calibration report or certificate. ISO/IEC 17025 specifies what must be in a calibration certificate (Clause 7.8.4), including the results, the uncertainty, the conditions, the standards used, and any adjustments or corrections applied. The certificate may list the instrument’s errors at various test points and often does not declare the instrument “pass” or “fail” – unless the lab was asked to include a statement of conformity to a spec. It’s important for lab managers to understand that a calibration certificate could show that an instrument is out-of-tolerance without explicitly saying “fail” (unless a verification step or tolerance evaluation is included)​. It then falls to the equipment owner (the lab) to decide if the instrument can be used as-is, needs adjustment, or is unsuitable, based on those results.

Verification is a related but distinct concept. ISO/IEC 17025 (through the VIM) defines verification as the provision of objective evidence that a given item fulfills specified requirements. In plain language, verification is about checking and confirming that something (an instrument, a method, a material, etc.) meets a defined specification or performance standard. For laboratory instruments, verification typically means confirming that the equipment’s performance is within the allowable tolerance or meets the manufacturer’s claims or any requirements for its intended use.

Key aspects of verification for equipment include:

• It is a check against criteria – you verify compliance with specific requirements. For example, if a pipette is supposed to deliver 100 µL ± 0.5 µL, a verification test would confirm whether the pipette actually delivers volumes in that range. If after testing, the pipette delivers 100 µL with an error of 0.2 µL, the verification passes (requirements fulfilled). If it’s off by 1 µL, the verification fails (requirements not met).
• It may use similar techniques as calibration (comparison to standards or measuring performance), but the goal is simply to confirm acceptability, not to fully characterize the error at multiple points. Verification is often a simpler check, sometimes an “abbreviated” calibration focused on the points or parameters of interest​. For instance, you might verify a thermometer by checking it at 0°C (ice point) and 100°C (boiling point) to see if it reads those correctly within tolerance – rather than calibrating it across a full range with uncertainty analysis. In doing so, you are using known reference points to test the thermometer, but you might not calculate the measurement uncertainty of the readings during this routine check.
• Traceability in verification: Ideally, the tools or references used for verification should themselves be calibrated (traceable), so that you have confidence in the check. ISO 9001:2015 actually allows that measuring equipment shall be calibrated or verified, or both, at specified intervals… against measurement standards traceable to international or national standards. This implies that verification should be done with reliable references. However, verification typically does not establish a new traceability link for the instrument under test; it relies on the existing traceability of whatever reference or method you use. The focus is on whether the instrument’s performance remains acceptable.
• Documentation: The results of a verification should be recorded, but they might be documented in a simpler form than a full calibration certificate. For example, a lab might keep a log of daily balance check readings showing the balance is within ±0.1 mg using a check weight – this serves as evidence of verification. In formal cases (like legal metrology or regulatory compliance), a verification certificate might be issued (for instance, a weights and measures inspector verifying a retail scale will apply a seal or sticker indicating it passed verification). ISO/IEC 17025:2017 requires labs to retain evidence of verification that equipment conforms with specified requirements, which could be records of test results, checklists, or certificates demonstrating that verifications were performed and the criteria were met.

One way to think of calibration vs verification is: calibration finds out “how wrong” an instrument is, while verification checks if it’s “wrong beyond an acceptable limit”. Calibration yields detailed measurement data (which can be used for adjustment or error correction), whereas verification yields a yes/no or pass/fail decision against a requirement. In practice, verification often follows calibration – you calibrate an instrument, then verify (compare the results to tolerances) whether it meets the required specifications. Indeed, the VIM notes explicitly: Calibration is a prerequisite for verification, which provides confirmation that specified requirements (often maximum permissible errors) are met.

To clarify with an example: if you send a device to a calibration lab, they will perform a calibration (compare it to standards and determine its error). Then, if you have defined acceptance criteria (say the device must be within ±1% of reading), the lab or you will verify whether the calibration results satisfy that tolerance. If yes, the device is “in spec”; if not, it’s “out of spec”. The calibration lab might report this as a statement of conformity if requested. If the device is out of spec, you might then adjust or repair it and calibrate again. If it’s in spec, you simply continue using it. Verification thus ties the calibration data to a compliance decision​.

Key points about verification:

• Purpose: To ensure that an instrument is fit for purpose and in compliance with specified requirements. It provides confidence that the equipment can produce valid results during its use. This is crucial for quality management, as using equipment that no longer meets requirements can lead to faulty test results. ISO/IEC 17025 emphasizes this by requiring verification of equipment before use (e.g. after maintenance or transport) to confirm it works as intended (Clause 6.4.4). Verification is about validating performance in practice – often done between formal calibrations or whenever there’s a need to prove the equipment still performs well.
• Process: Often a simplified test or check. It might be done by laboratory staff internally. For example, a lab might perform a daily verification check on a balance using a standardized weight: if the balance reads the 50.00 g check weight within ±0.1 g, it passes that day’s verification. This process is quick and meant to detect any significant drift or problems as they arise. Another example is verifying a temperature oven’s setpoint by placing a calibrated data logger inside and seeing if the oven’s display is within an acceptable range of the actual temperature. Verification procedures are usually documented in the lab’s quality system (ISO 17025 requires that intermediate checks/verification be done according to a procedure​). They may not cover every detail that a full calibration would, but they focus on critical parameters that need to stay in control.
• Traceability & Uncertainty: While a routine verification might not explicitly calculate uncertainty, any reference used (like a check weight or thermometer) should be traceable so that the evidence is reliable​. If an uncertainty evaluation is needed (say to ensure a tight tolerance is met), it can be included, but commonly verification is treated as a go/no-go check with known good references. The VIM notes that when applicable, measurement uncertainty should be taken into consideration in verification​ – meaning if the margin is small, you do need to account for uncertainty even in a verification to avoid wrongly passing a failing instrument or vice versa.
• Documentation: Verification results are typically documented in simpler records than calibration. This could be a form that indicates the item, date, reference used, points checked, results, and a judgment of “meets requirements” or not. These records should be retained as part of the quality system (ISO 17025 clause 6.4.13(c) calls for retaining records of verification for equipment affecting laboratory activities​). Unlike calibration certificates, verification records might be internal documents and often do include a clear statement of whether the item was acceptable. For example, after an intermediate check (a term ISO 17025 uses for verifications between calibrations), a lab may record “Oscilloscope XYZ verified on 2025-04-19 against 1 V and 5 V DC standards, results within tolerance ±0.5%, instrument acceptable for use” – providing evidence of continued control.

It’s worth noting that verification in ISO/IEC 17025 can also refer to other contexts – e.g. verifying methods or results – but in this guide we are focusing on equipment verification. Also, do not confuse verification vs validation: in ISO terminology, validation is a special case of verification where the goal is to prove the item is adequate for an intended use​ (for instance, validating a new test method). Not every verification is a validation. For equipment, when we say verification we usually mean routine performance checks, whereas validation would be more relevant to methods or non-standard measurements.

Now that we have defined each term, let’s summarize the key differences between calibration and verification. While both are quality assurance activities under ISO/IEC 17025, they differ in their purpose, scope, and application:

• Purpose: Calibration is aimed at determining the accuracy and precision of an instrument by quantifying its errors and uncertainties. It answers the question, What is the true value and uncertainty corresponding to this instrument’s reading? Verification, on the other hand, is aimed at ensuring an instrument meets a specific requirement or tolerance. It answers, Is this instrument’s performance acceptable (yes/no) according to the defined criteria? Calibration data helps you understand an instrument’s behavior; verification gives you confidence that the instrument is fit for use in its intended application.
• Process: Calibration involves a thorough comparison against reference standards across the needed range, often multiple test points, and includes analysis of uncertainties​. It may be time-consuming and is usually performed on a schedule (e.g. annually) or after events like repairs. Verification is generally a simplified check – it might use one or a few points to confirm performance, and usually does not involve the full rigor of uncertainty evaluation each time​. Verification can be performed more frequently (e.g. daily, weekly, or before each use, depending on need) because it’s quicker. For example, calibrating a balance might involve checking linearity at 5-6 different masses and calculating uncertainty, whereas a daily verification might just be placing one standard weight to see if today’s reading is OK. Verification often follows calibration in practice: you calibrate first to know the values, then verify regularly to ensure nothing has changed beyond acceptable limits​. If during verification you find a problem (instrument no longer within spec), you then know a recalibration or adjustment is needed.
• Traceability: Calibration provides the formal traceability chain – the calibration certificate links the instrument to national/international standards through an unbroken chain of comparisons​. It’s an essential part of establishing metrological traceability for measurements (ISO 17025 requires traceability for all measurement results that affect test/calibration outcomes). Verification relies on traceability of whatever reference is used for the check, but it typically does not extend the traceability chain of the instrument under test by itself. In other words, calibration updates the instrument’s known relationship to SI units (often assigning correction factors or confirming its accuracy), while verification ensures the instrument still behaves within the allowed range since the last calibration. Both activities should use calibrated references, but full traceability documentation is emphasized in calibration. As a rule of thumb, if an instrument has never been calibrated, simply “verifying” it with an unknown reference would be meaningless – you need that initial calibration to know its true performance. Verification maintains confidence between calibrations, not in place of calibration when one is required​.
• Output & Documentation: Calibration yields quantitative results – typically a report of measured values, uncertainties, and perhaps adjustments made. It may or may not include a pass/fail statement to specs. The documentation (calibration certificate) is usually quite detailed and is often required by auditors or customers as evidence of instrument accuracy. Verification yields a qualitative result – essentially a confirmation (or not) that specified requirements are fulfilled. Documentation of verification might be a simple form or record noting that the check was done and whether the item met the criteria. For example, a verification record for a pipette might state it dispensed volumes within tolerance at 3 tested points. There is typically no uncertainty stated (unless needed to interpret the results) and no comprehensive data on every aspect of the instrument’s performance – just the evidence relevant to the specification. Verification records are important for internal quality control and to demonstrate compliance with ISO 17025 clauses that require showing equipment is suitable. But they are generally not shared outside the lab unless requested or during audits.
• Frequency & Timing: Calibration is usually performed at scheduled intervals (based on manufacturer recommendation, usage frequency, stability history, etc.) or after certain events (repair, mishandling, or when an instrument is found or suspected to be out of tolerance). Verification can be done much more frequently: for critical instruments, many labs do “intermediate checks” (ISO 17025’s term for verifications between calibrations) at defined intervals to catch any drift early​. For instance, a thermometer used in a daily process might be formally calibrated once a year, but verified monthly against a reference thermometer. The need for intermediate verification is determined by how stable the instrument is and the risk if it goes out of spec. ISO 17025:2017 specifically states that “when intermediate checks are necessary to maintain confidence in the performance of the equipment, these checks shall be carried out according to a procedure” (Clause 6.4.10). Lab managers should assess each instrument and decide if periodic verification between calibrations is required (many accreditation bodies expect to see evidence that this has been considered).
• Expertise: Calibration often requires specialized knowledge, equipment, and possibly an external accredited calibration provider (especially for high-accuracy or complex calibrations). Verification can often be done in-house by trained technicians or lab staff since it may involve simpler tests. For example, you might send your weights to a metrology lab for calibration, but your technicians can verify the weighing balance daily using those calibrated weights. Verification activities still require training and defined procedures, but they usually don’t require the full metrological expertise that an accredited calibration does.

In summary, calibration is a measurement process that characterizes an instrument, while verification is a check that assures the instrument is still adequate for use​. Both are essential: calibration underpins the accuracy (with traceability and data), and verification maintains confidence in between calibration events or confirms suitability. ISO/IEC 17025 treats them as distinct concepts and even cautions in the standard’s notes not to confuse the two.

To illustrate when each activity is applicable, here are some common laboratory scenarios:

• Analytical Balance (Mass Measurements): A precision analytical balance in a chemical lab is typically calibrated once a year by an accredited calibration service. The calibration involves using a series of traceable weights across the balance’s range (e.g. 1 g, 10 g, 100 g) to determine its accuracy and linearity, and the calibration certificate reports the balance’s errors (and perhaps uncertainty) at those points. Between these annual calibrations, the lab performs verification checks daily or weekly: a known check weight (say 50.000 g) is placed on the balance each morning to verify that the reading is within an acceptable tolerance (e.g. 49.997–50.003 g). If the balance fails the daily verification (reading too high/low), the lab knows something is wrong – it might need recalibration or service before its due date. This routine verification ensures ongoing confidence that the balance is working correctly and prevents the scenario of using a misreading balance for months. In ISO 17025 terms, the formal calibration establishes traceability and accuracy​, while the intermediate checks (verification) maintain confidence in the calibration status​. The balance’s records will include the annual calibration certificate and a log of daily verification results.
• Thermometer or Temperature Logger: Consider a digital thermometer used to monitor freezer temperature in a clinical lab (where samples must be kept below -20°C). The thermometer is calibrated (perhaps at -20°C and 0°C points) by a calibration lab to ensure its readings are accurate, with a certificate stating its error (e.g. at -20.0°C true, it reads -19.5°C, so it has a +0.5°C bias with some uncertainty). This calibration is done annually. However, because of the critical nature of sample storage, the lab also performs a verification monthly: they place the thermometer in an ice bath (0°C reference point) or use a secondary calibrated thermometer to cross-check the freezer reading. If the device reads within, say, 0.2°C of the reference, it passes verification. This way, if mid-year the thermometer starts drifting (maybe it suddenly reads 3°C too warm), the monthly check will catch it – prompting immediate action before any samples are ruined. This example highlights compliance and quality: a drift caught by verification can save the lab from unknowingly storing samples at the wrong temperature. In regulated industries, such early detection via verification can prevent costly recalls or safety issues​.
• Volumetric Pipette: A lab has a 100 µL micropipette used for dispensing fluids in tests. Calibration of the pipette might be performed twice a year in-house: a trained technician weighs distilled water dispensed by the pipette (using a calibrated balance) to determine the actual volume delivered (using water’s density). They do this at 100 µL and perhaps 50 µL, calculate the error and uncertainty, and adjust the pipette if necessary to correct any bias. A certificate or record is produced showing, for instance, after adjustment the pipette delivers 100.0 µL with ±0.3 µL uncertainty. Between these calibrations, the lab does a quick verification check quarterly: dispense 100 µL of water and check the weight – if it’s within an allowed tolerance (e.g. within ±1 µL of target, given the process requirements), the pipette is verified okay. If not, it might be taken out of service for recalibration. This ensures the pipette remains reliable for use. Here, calibration provided the accurate baseline and uncertainty for the pipette, and periodic verification ensures it stays within allowable error for the lab’s needs.
• Pressure Gauge: In an industrial equipment testing lab, a pressure gauge is used to measure pressure in test setups. It is calibrated every 2 years across 5 pressure points by an external lab, with a full report of its readings vs true pressure and an uncertainty of ±0.5% FS. The lab also performs an in-house verification before critical tests: they connect the gauge to a calibrated pressure reference or deadweight tester at one key pressure (say 100 psi, which is near the typical operating point) and verify the gauge is within the required tolerance (perhaps ±1 psi). This 5-minute check before the test campaign starts can prevent using a misreading gauge. If the gauge fails, they replace it or get it calibrated. ISO 17025 Clause 6.4.4 actually requires such an approach – verifying equipment conforms to specifications before being placed into service or back into service​ (for example, after you get a gauge back from repair, you should verify it works correctly before using it in your lab tests).

These examples demonstrate a general principle: Calibration is done to establish performance and traceability, whereas verification is done to quickly confirm ongoing validity or suitability. Both are important in a laboratory’s quality system. Calibration without verification can lead to long gaps where instrument drift goes undetected; verification without an initial calibration can be meaningless because you wouldn’t have accurate references or baseline data.

Understanding the difference between calibration and verification is not just academic – it has real consequences for compliance, quality, and risk management in the lab. ISO/IEC 17025:2017 expects labs to manage both properly, and auditors will look for evidence that you calibrate and/or verify instruments appropriately.

From a compliance standpoint: if you misinterpret these terms, you might inadvertently fail to meet the standard’s requirements. For example, ISO 17025 requires that measuring equipment that significantly affects test or calibration results must be calibrated (Clause 6.4.6) when accuracy or traceability is needed. If a lab manager thought a simple functional check (verification) of an instrument was a substitute for calibration in all cases, they might not establish traceability for that instrument – leading to a nonconformance. Conversely, the standard also allows for equipment verification in appropriate cases: ISO 9001 and ISO 17025 both recognize that some equipment can be “calibrated or verified, or both” to ensure valid measurements​. The key is knowing when each is appropriate. Regulators and accreditation bodies want to see that you have a sound rationale for your calibration/verification program. This typically means: all critical instruments are calibrated at suitable intervals, and interim verifications (intermediate checks) are in place where needed to maintain confidence. Records should reflect both activities (e.g. calibration certificates on file and logs of verifications performed)​.

From a quality management standpoint: having clarity on these concepts ensures your team knows how to maintain the accuracy of measurements day-to-day. Calibration and verification together form a feedback loop for quality. Calibration provides the accuracy baseline, and verification provides ongoing control. If either is neglected or misunderstood, the lab risks making incorrect measurements. For instance, if a manager assumes that a calibrated sticker on an instrument guarantees it’s always right, they may skip verification – and as discussed, the instrument could drift out of spec in between calibrations, undermining all results produced in that period​. On the other hand, performing verifications diligently can catch problems early: “if you only perform calibration annually…and the device comes back out of calibration, how can you trust the measurements since the last calibration? Every measurement since its last calibration is now suspect.”​ This scenario from a Fluke Calibration note highlights that relying solely on infrequent calibrations can be risky; regular verification checks can significantly lower that risk by alerting you to issues closer to real-time​. Especially in industries like pharmaceuticals, food, or aerospace, using an instrument that has slipped out of tolerance can have serious regulatory and safety consequences – products could be recalled, or health and safety could be jeopardized​. Thus, robust verification practices are a form of risk mitigation.

Moreover, clear understanding of these terms aids in effective communication. Lab managers often need to explain to staff why certain equipment needs to be sent out for calibration versus what checks can be done in-house. They also need to interpret calibration certificates (which might list raw error values) and translate that into a decision: “Is this tool okay to use?” Knowing that the certificate alone isn’t a pass/fail verdict is important – you have to perform that verification step of comparing to acceptance criteria. In one real-world example, a company had a coordinate measuring machine (CMM) calibrated and received a certificate with the measurement data, but no tolerances or conformance statement. The staff assumed “calibrated” meant “good to go” and continued using the CMM, but an auditor later pointed out the data showed the CMM was out of tolerance, leading to months of potentially bad measurements​. The lesson for managers is that calibration results must be reviewed against requirements – either by having the calibration supplier include a verification (conformance) or by checking it yourself – otherwise calibration alone doesn’t guarantee quality. Understanding verification ensures you don’t overlook that critical step.

ISO/IEC 17025 also explicitly links these activities to the management system. For example, when equipment is found out of spec, the lab must take action (such as removing it from service and assessing the impact on past results per Clause 6.4.9). Knowing the status of equipment through calibration and verification records allows managers to make informed decisions and show auditors that any issue is caught and addressed promptly (thus maintaining confidence in reported results).

In summary, proper use of calibration and verification is essential for maintaining measurement integrity. It ensures that results reported to customers are valid and defensible. It also optimizes costs and effort: calibrate when you need the detailed info or traceability, verify in-between to avoid unnecessary calibrations and to catch drift. A well-structured program that balances calibration and verification demonstrates compliance with ISO 17025’s emphasis on valid results and continual control of laboratory processes​.

The 2017 version of ISO/IEC 17025 brings a risk-based approach but continues to have clear requirements regarding calibration and verification of equipment. Laboratory managers should be particularly mindful of the following clauses in ISO/IEC 17025:2017:

• Clause 6.4.4 – Verification of Equipment Performance: “The laboratory shall verify that equipment conforms to specified requirements before being placed or returned into service.”. This means whenever you acquire new equipment, or after it’s been repaired or calibrated and comes back, you need to verify it meets the necessary specs before using it for lab work. For instance, if your microscope was serviced, you might verify its calibration or alignment before putting it back to routine use. This clause underscores the importance of verification as a gatekeeper to ensure only suitable equipment is used.
• Clause 6.4.6 – When Calibration is Required: “Measuring equipment shall be calibrated when: the measurement accuracy or measurement uncertainty affects the validity of the reported results, and/or calibration of the equipment is required to establish the metrological traceability of the reported results.”​. This gives two clear criteria: if the accuracy/uncertainty matters for your results, or if you need that equipment to be traceable, you must calibrate it. The standard also provides a note with examples of equipment types that need calibration (e.g. instruments that directly measure the test item, those used to correct values, etc.). Essentially, any critical measuring tool that influences your test or calibration outcome should have a proper calibration. Lab managers should inventory their equipment and identify which items fall under this requirement – those will need calibration schedules.
• Clause 6.4.7 – Calibration Programme: “The laboratory shall establish a calibration programme, which shall be reviewed and adjusted as necessary in order to maintain confidence in the status of calibration.”. This means you should have a documented plan for calibrations (frequency, methods, etc.), and you should adjust it based on experience (for example, if an instrument is very stable you might lengthen its interval, or if one starts drifting you might shorten the interval). This programme is part of the lab’s quality system and ensures no required calibration is overlooked.
• Clause 6.4.8 – Labeling of Calibration Status: It requires that equipment that needs calibration or has a validity period be labeled or coded to allow users to know its status​. In practice, this is the calibration sticker or identification in your system that shows when the last calibration was and when the next is due. While not directly about verification, it’s related – some labs also label equipment with verification status or dates of last check (especially if certain equipment is only verified, not full calibrated).
• Clause 6.4.9 – Out-of-Spec Equipment: If equipment is found to be defective or outside requirements (e.g. fails a verification or is damaged), it “shall be taken out of service… until it has been verified to perform correctly”. This clause connects verification to corrective actions: whenever an instrument is suspect (maybe a failed check or physical damage), you must remove it from use and verify it after correction before using it again. Also, you need to evaluate if the out-of-spec condition impacted any results and handle those per the nonconforming work process. The standard here reinforces that simply fixing or calibrating the instrument isn’t enough – you verify it is now working acceptably (and document that) before reinstating it.
• Clause 6.4.10 – Intermediate Checks: “When intermediate checks are necessary to maintain confidence in the performance of the equipment, these checks shall be carried out according to a procedure.”​. The standard expects labs to perform interim verifications (checks) on equipment if needed. It doesn’t prescribe how often – that’s up to the lab’s judgment based on the equipment’s stability and usage – but it does require that if you do them, you must have a proper procedure. Typically, a procedure will outline how to do the check, what reference to use, acceptance criteria, and what to do if it fails. Auditors will often ask: “How do you know this instrument remains okay between calibrations?” If your answer is “we do intermediate verifications monthly” – they will then check that there’s a written procedure and records for those checks.
• Clause 6.5 – Metrological Traceability: This clause ties into calibration. It requires that measurement results be traceable to SI units through a documented unbroken chain of calibrations​. In practice, this means all calibrations must be done either by a competent (usually accredited) lab or using nationally recognized standards. If you choose to rely on verification in lieu of calibration for certain equipment, you need to be careful – the clause allows traceability to be established via calibration. Verification alone (without an initial calibration) might not fulfill traceability unless the “verification” is essentially a calibration by another name. So ensure that any equipment that needs traceability is indeed calibrated appropriately. Verification supports traceability by confirming continued validity, but doesn’t create traceability from scratch.
• Clause 6.4.13 – Equipment Records: This clause lists what records to keep for equipment. Notably, it includes “evidence of verification that equipment conforms with specified requirements” (6.4.13 c) and also records of calibration dates, results, adjustments, acceptance criteria, and due date of next calibration (6.4.13 e). This means your lab’s equipment files should contain both calibration certificates and any verification records applicable. During an ISO 17025 audit, the assessor may pick a piece of equipment and ask to see its file – they will expect to find calibration documentation and perhaps verification logs (and evidence that when the item was received or put into service, you verified it per 6.4.4). Ensure these records are organized and retained for the period required.
• Clauses 7.2 and 7.7 – Method Verification & Measurement Uncertainty: While not directly about equipment calibration, ISO 17025 also discusses method verification/validation and measurement uncertainty evaluation. They are related in the sense that using calibrated equipment with known uncertainty feeds into method accuracy and overall uncertainty. A method verification (7.2) confirms a lab can properly perform a standard method – this might involve verifying the equipment used in the method is calibrated. And clause 7.7 requires the lab to evaluate measurement uncertainty for results – which relies on knowing the calibration status and performance of instruments. So, good calibration practices for equipment are foundational for meeting these broader requirements.

In essence, ISO/IEC 17025:2017 expects labs to have control over their measuring equipment. Calibration and verification are the twin mechanisms of that control. Calibration establishes the measurement capability, and verification checks that capability is maintained. By following the standard’s requirements for both, a lab demonstrates competence in generating valid results.

Even experienced lab managers can stumble over calibration vs verification nuances. Here are some common misconceptions or errors – make sure you and your team avoid these:

• Assuming “Calibrated” Means “In Tolerance”: As discussed, a calibration process by itself might not include a pass/fail evaluation. It’s a data-gathering exercise. A big mistake is to see a calibration sticker within date and automatically assume the instrument is fine. Always review the calibration results or have a verification step for tolerances. If you don’t specify acceptance criteria to your calibration provider, you may get a certificate with numbers but no judgment. It’s then your responsibility to compare those numbers to the instrument’s allowed limits. Ignoring this step can lead to using out-of-tolerance equipment unknowingly. The CMM example earlier is a case in point, where lack of tolerance analysis after calibration led to months of inaccurate measurements. Tip: When sending equipment for calibration, consider asking for a statement of conformity to spec, or immediately verify the returned data against specs. Never just file the certificate without review.
• Using the Terms Interchangeably: Some personnel might say “we calibrated that stopwatch by checking it against the internet time” – what they actually did was a verification (and likely not a formal calibration with uncertainty). It’s important not to label routine checks as full calibrations. Auditors can tell the difference. Misusing terminology can cause confusion in procedures and records. Keep the language consistent: e.g. daily “verification checks” or “performance checks” vs. annual “calibration.” ISO 17025 itself cautions that verification should not be confused with calibration. By maintaining this distinction, you’ll also be clear on what documentation is needed for each.
• Believing Calibration Includes Adjustment: Many think that when an instrument is “calibrated,” it’s automatically adjusted to zero error. In reality, calibration is often performed without adjustment – it’s measurement first. Adjustment (alignment/tuning) is a separate operation that may or may not be done as part of a service. The VIM notes explicitly: “Calibration should not be confused with adjustment of a measuring system”​. If you send a device for calibration and it comes back with a certificate, don’t assume it was adjusted unless the certificate or service report says so. Always check: if it was out of tolerance and they didn’t adjust it, the certificate’s data will show that. Some calibration providers will adjust the instrument if possible (and list it on the report), others only calibrate and leave adjustment to be authorized separately. Mistake to avoid: not clarifying with your vendor whether adjustment is included, and not checking if your instrument came back within spec or still needs fixing.
• Neglecting Measurement Uncertainty in Calibration: Calibration is not just comparing to a standard; it must include an uncertainty analysis to be meaningful in ISO 17025 terms. A misconception is that as long as you check against a standard, you’re calibrated. If your calibration documentation lacks uncertainty, you actually don’t know how reliable the comparison is. For example, calibrating a thermometer with a reference of the same accuracy without accounting for uncertainty could give a false sense of security. The proper approach would consider the reference’s uncertainty, environmental factors, repeatability, etc. As one reference puts it: if you don’t include uncertainty and traceability, “you are just performing a simple verification” not a true calibration​. So, avoid any “calibration” procedures in your lab that do not calculate uncertainty or at least establish a realistic tolerance based on it. This is both a metrological mistake and an ISO 17025 compliance issue (since the standard requires reporting of uncertainty in calibration certificates where applicable).
• Over-reliance on Calibration Interval without Ongoing Checks: It’s a mistake to set a calibration interval (say 1 year) and then never check the instrument in between. Even high-quality instruments can drift or fail. If you only discover an issue at the next calibration, all the work done since the last calibration might be compromised. This is why ISO 17025 allows and encourages intermediate verifications. A common pitfall is thinking “the cal interval is 1 year, so we don’t need to worry about it until then.” In reality, you should periodically ask “is this interval still appropriate?” and use verification data to adjust if needed​. If verifications show the instrument is always well within tolerance, maybe the interval can be extended (saving cost and downtime). If verifications catch drift, you might shorten the interval or service the instrument sooner. Not doing verifications at all means you’re essentially blind to issues between calibrations. Avoid the “calibrate and forget” mindset; instead, adopt a “calibrate and monitor” approach.
• Ignoring Verification Because of Trust in Calibration Labs: Some managers might think, “We send everything to an accredited lab, so we don’t need to verify anything ourselves.” While accredited calibration provides high confidence, ISO 17025 still mandates verification in certain situations (6.4.4, 6.4.9, 6.4.10 as noted). Also, things can happen during transportation or installation. It’s wise to verify critical functions when equipment returns from external calibration – not because you doubt the calibration lab, but to ensure nothing changed during shipping or to double-check it meets your specific needs. For instance, you got a balance calibrated; upon return you verify it with a check weight in your lab environment to confirm it still reads correctly on your bench (perhaps leveling or local gravity differences could have minor effects). This extra step can catch any discrepancies. So don’t skip verifications entirely just because a calibration was done; they serve slightly different purposes.
• Confusing “Verification” in Different Contexts: Make sure not to mix up equipment verification with method verification or validation. ISO 17025 uses verification in multiple contexts. Method verification (verifying that a standard method works in your lab) is different from verifying an instrument’s performance. Some might erroneously treat a method validation as also covering the instrument, but instruments need their own checks. Conversely, a verified instrument doesn’t mean a method is verified for a sample matrix. Keep these QA activities separate in planning and documentation.

By avoiding these common mistakes, lab managers can improve their lab’s reliability and ensure they meet ISO/IEC 17025 requirements. Always foster a culture where technicians and staff understand why they are doing a calibration or a verification. When everyone knows the purpose and limitations of each, the laboratory as a whole will be better positioned to produce consistently valid results.