Instrument calibration is a critical part of your business to ensure your product quality and reliability. But do you know how to select the right provider for your business? Do you have the prior knowledge you need to make informed choices?
In this comprehensive guide to calibration services:
- Find out what calibration services are.
- Understand calibration concepts in depth.
- Learn about calibration standards and accreditation.
- Learn about the benefits of Keysight’s one-stop multi-brand calibration services.
What Are Calibration Services?
Calibration services ensure the accuracy and reliability of measuring instruments and test systems.
Calibration services typically conduct these four steps on an instrument or system:
- Instrument inspection: The device is thoroughly inspected to assess its current state.
- Calibration testing: The device is subjected to a comprehensive suite of performance tests that compare its measurements against known standards to check if they’re within the promised specifications.
- Adjustments and corrections: If any errors are detected during the calibration tests, adjustments are made to bring the measurements within specification. This is done by tuning circuit parameters and software configuration inside the instrument.
- Calibration certificates: After successful calibration, a detailed calibration certificate is provided to the customer.
The concepts mentioned here are explained further under “Understanding Calibration.”
Who Offers Calibration Services?
Calibration services are offered by calibration service providers. These could be:
- Businesses that specialize in calibration services (also known as “cal labs”)
- Original equipment manufacturers (OEMs) of instruments
- Nationalmetrology institutes (NMIs) of different countries
- In-house calibration labs or departments of companies
Understanding Calibration

Before choosing your calibration service providers, you must understand the key concepts that will influence your choices. Here are some overviews of calibration concepts and theory for readers unfamiliar with them.
What Is Calibration?
For any phenomenon, its model implicitly assumes that every model parameter has a true value at every instant. To get reliable predictions, your measurement of each parameter must be close to its instantaneous true value.
You can express this idea of closeness using three concepts:
- Accuracy: It tells you how small the differences between measured and true values will be as a percentage of the true value. These differences are called errors.
- Precision: It tells you how consistent the measurements will be.
- Uncertainty: Uncertainty is a quantification of the inherent doubt in each measurement. Quantifying uncertainty lets us unambiguously specify how confident we are about the accuracy.
Calibration is the process of comparing the output of a measuring instrument, sensor, or test equipment against a known reference standard to determine if its performance is within promised specifications.
Why Should You Calibrate?
In practice, the calibration process not only compares a device to a standard but also tunes it for accurate and reliable measurements. This is an essential precondition for:
- Quality control: Accurate measurements are essential for quality control in industries like aerospace and semiconductors.
- Safety: Accurate measurements are critical for safety in many applications. Inaccurate measurements of pressure could lead to accidents or equipment failure.
- Compliance: Calibration is mandatory for regulatory and industry compliance. For example, in the food industry, temperature-measuring devices must be calibrated regularly to ensure that food is stored safely.
- Preventive maintenance: You can extend the life of your devices and reduce the costs of buying new devices.
- Avoiding hidden costs: Inaccurate measurements may lead to business consequences like reputational damage, loss of customer loyalty, regulatory penalties, or legal costs.
How Often Should You Calibrate?
The ideal calibration frequency is decided by general guidelines as well as business-specific and environment-specific recommendations.
General guidelines include:
- Manufacturer’s recommendations: Follow the schedule given by the device manufacturer. This is typically monthly, quarterly, or annually.
- Regulatory requirements: If your local regulations specify an interval, follow them.
- Industry norms: If your industry as a whole recommends certain intervals, follow them.
Some project-specific factors to consider are:
- Project criticality: Decide an interval based on the criticality of the project and its quality thresholds.
- Frequency of use: Equipment that is heavily used daily is likely to drift more frequently. Consider this factor to decide the interval.
- Conditions of use: Devices that are subject to rough handling or difficult environments require more frequent calibration.
Understanding Uncertainty

Uncertainty is essential to the calibration process, the metrology standards, accreditation, and the selection of calibration providers.
What Is Uncertainty?
Uncertainty quantifies the inherent doubt in a measurement.
We call it inherent because you can never fully eliminate uncertainty, merely account for it. This becomes clear when we examine some of the sources of uncertainty:
- Instrument and component errors: Instruments and their internal components are always drifting away from specifications due to aging, wear, electrical noise, and other natural phenomena.
- Environmental effects: The quantity being measured may be inherently affected by temperature, humidity, quantum effects, chemical reactions, or other processes in its environment.
How does uncertainty help? We can quantify measurement doubt using an uncertainty and confidence level. For example, if the uncertainty of a multimeter is ±0.1 volts with 95% confidence, it means for 95% of all measurements, the displayed voltage will be within 0.1 volts of the true value.
Uncertainty helps us decide if an instrument is out of specification. The illustration below shows the measurement possibilities for a two-sided specification with an uncertainty
How Is Uncertainty Calculated?
According to the International Organization for Standardization’s (ISO) Guide to the Expression of Uncertainty in Measurement (GUM) standard, uncertainty is calculated as follows:
- Identify the quantity to be measured (the measurand).
- Model the measurement by expressing the measurand as a function of related quantities.
- Derive an uncertainty equation from the measurement equation.
- Evaluate the measurement and uncertainty equations.
What Are Guard Bands?
Guardbanding is a technique to account for the uncertainty risk in the calibration and adjustment process.
If a measurement falls slightly outside specification due to the uncertainty, there’s a non-zero risk that the device is operating out of specification some of the time. But this risk, no matter how small, may be unacceptable in some industries and use cases.
To account for it, the effective acceptance zone is narrowed by the same amount as the uncertainty at both ends so that every measurement is always within specification. This reduction at each end is called the guard band.
The rest of the calibration and adjustment process is then conducted within this narrowed acceptance zone.
What Is the Calibration Process, and What Are the Key Steps?
The key steps of the calibration and adjustment process are depicted below.
Let’s understand each of these steps.
Step 1: Run Performance Verification Tests
Performance verification runs a comprehensive set of device-specific tests to measure its actual performance on every specification and enabled functional option.
For example, the below image shows the performance verification tests run by the Keysight N7814A X-Series SignalAnalyzer Calibration Application for N9000A CXA signal analyzer:
Step 2: Did All Verification Tests Pass?
The results of the tests are evaluated to identify which tests passed, failed, or partially failed.
If all the tests pass, the device is successfully calibrated, and nothing more is necessary.
But if some tests fail, you should run the adjustments tests.
Step 3: Run Adjustment Procedures
The adjustment procedures tune the device by adjusting various circuit parameters and components, and, sometimes, by resetting or recalculating some correction values.
Note: Never run adjustment procedures routinely as if they’re calibration tests. Run them if and only if some verification tests fail.
The illustration below shows the available adjustments for the N9000A CXA signalanalyzer.
Step 4: Did All Adjustments Run Correctly?
If all the adjustment pass, rerun the performance tests. However, if any adjustment fails, repair the device.
Step 5: Repair the Instrument
During this step, identify the reasons for the failed adjustments. If a faulty component is detected, order and install new parts. Then, repeat the adjustment process in step three.
Step 6: Generate the Calibration Reports and Certificates
The last step is the generation of a calibration report with all the information requested by the customer. One or two reports are generated depending on whether adjustments were required:
- As-received report: It has all the results of the initial set of performance verification tests.
- As-completed report: If adjustments were needed, it has all the results of the adjustments and subsequent performance tests.
The reports include calibration certificates that describe:
- Identification details of the instrument and date of calibration
- The calibration procedure followed
- The standards used
- Traceability table (explained later)
The certificates are evidence that the instrument has been calibrated and is traceable to international standards.
An example calibration certificate is shown below.
To understand some of the details in these reports, we must first understand the various standards, the worldwide metrology ecosystem, and concepts like accreditation and traceability.
You should know all the key standards to ensure reliable calibration, select good calibration service providers, and comply with regulations and norms.
ISO/IEC 17025
The ISO/IEC 17025 is an international standard that specifies requirements for testing and calibration laboratories. They include:
- Technical requirements on test equipment, calibration processes, and test procedures
- Quality management and control procedures
- Reporting protocols, including identifying and reporting all sources of uncertainty
- Recommended competencies for personnel
- Organizational conditions to ensure impartiality
IEC 17025:2017 is its latest version, superseding the 2005 version.
ISO GUM
The Guide to the Expression of Uncertainty in Measurement is dedicated to uncertainty in measurement, covering:
- Identification of sources of uncertainty
- Calculation and expression of uncertainty without ambiguity
ILAC-G8 and ILAC-P14
The International Laboratory Accreditation Cooperative (ILAC) publishes international guidelines and policies for accreditation bodies and calibration laboratories.
Its ILAC G8:09/2019 Guidelines on Decision Rules and Statements of Conformity provide guidance to calibration laboratories in the use of decision rules when issuing statements of conformity as required in the ISO/IEC 17025:2017. It also guides assessors, regulators, and customers to decide if a calibration report meets the requirements of standards.
Its ILAC P14:09/2020 ILAC Policy for Measurement Uncertainty in Calibration focuses specifically on the estimation and expression of uncertainty in calibration and is based on the ISO GUM.
ANSI/NCSL Z540.3
The ANSI/NCSL Z540.3-2006 is a U.S. national standard that specifies technical requirements for the calibration of measuring and test equipment. In 2020, it was withdrawn in favor of the ISO 17025:2017 but remains a recognized standard, and its certification is still offered by calibration service providers.
ANSI/NSCL Z540.1 and Z540.2
The ANSI/NCSL Z540.1-1994 is an older U.S. national standard for quality management systems of calibration laboratories. It was withdrawn in 2007 but is still recognized and offered as certification by calibration providers.
The ANSI/NCSL Z540.2-1997 is a U.S. national standard identical to the ISO GUM with minor changes in verbiage for the American audience. It was withdrawn in 2020 in favor of GUM.
The illustration below gives you an overview of how all these standards are related.
In summary:
- All national bodies have converged on the international ISO 17025:2017 and ISO GUM as the preferred standards for accreditation and certification.
- Older national standards are withdrawn in favor of ISO standards but continue to be recognized.
- All organizations related to calibration can use ILAC’s guidelines and policies to achieve ISO 17025 conformance.
Closely related to these standards are their certification and accreditation ecosystem.
Understanding the Worldwide Accreditation Ecosystem
The standards above are issued by a worldwide certification and accreditation ecosystem. Let’s understand accreditation and the organizations that participate in it.
What Is Accreditation?
Accreditation is the process by which an independent third party assesses an organization’s competence in calibration services and certifies its compliance with standards like ISO 17025 and ISO GUM.
Accreditation provides assurance that the calibration service provider is conducting those services according to globally recognized standards.
Accreditation is a stringent process. For example, accreditation to ISO 17025 involves verifying a provider’s technical competence — through proficiency testing and interlaboratory comparisons — to perform the work listed in the scope of accreditation.
Accreditation of a calibration service provider is beneficial to you as their customer:
- You can trust their capabilities, reliability, and quality.
- You can reduce the risks of errors and non-compliance.
The ecosystem of accreditation involves national metrology institutes, accreditation bodies, and calibration providers.
National Metrology Institutes
The NMIs provide measurement infrastructure, primary standards, and references in their respective countries. Examples include:
- National Institute of Standards and Technology in the U.S.
- National Physical Laboratory in the U.K.
- Physikalisch-Technische Bundesanstalt in Germany
The NMIs are responsible for developing national measurement standards and collaborating with other NMIs for global harmonization of measurement standards.
Accreditation Bodies
Accreditation bodies are independent, third-party organizations that assess the competence of certification bodies and testing laboratories. Accreditation bodies ensure that these organizations meet all the requirements of international standards like the ISO 17025.
Some examples of accreditation bodies:
- American National Standards Institute (ANSI) National Accreditation Board (ANAB) and American Association for Laboratory Accreditation (A2LA)
- United Kingdom Accreditation Service (UKAS)
- China National Accreditation Service (CNAS)
What Is Traceability?
Traceable calibration means connecting a measurement back to the standards of the international system of units through an unbroken chain of comparisons whose uncertainties are certified by calibration service providers. The conformity of those bodies can also be traced back to the national metrology institutes and accreditation bodies.
An example of a traceability table from a sample calibration report is shown below.
How to Choose a Reliable Calibration Service Provider
Here are some key questions and guidelines to help you decide your calibration workflow.
Should You Calibrate In-House or Outsource It?
Critical questions to ask when you can calibrate in-house:
- Can in-house calibration meet all your quality and regulatory requirements?
- Do you have people with expertise and time to calibrate? If you’re short on people or time, can you hire new people?
- Do you have the necessary test equipment, calibration software, and adjustment procedures?
- If the instruments are for a mission-critical project, can you take the risk of lower-quality calibration?
- Some industries like pharmaceuticals require quality management that is audited by regulators like the Food and Drugs Administration. Are you audited?
If your organization or department is considering outsourcing, key questions to ask are:
- Can you afford an external provider and their contractual terms?
- Can the external provider deliver the desired accuracy, quality, and service per your schedule?
- What’s the scope of accreditation issued to the calibration service provider? Does their scope of accreditation cover all the parameters and ranges required to calibrate your instruments? They should list parameters and ranges like this scope ofaccreditation issued to Keysight.
If Outsourcing, Should You Choose On-Site Calibration Services or Off-Site?
In on-site calibration, a calibration service provider brings their experts and equipment to your facility and performs the calibrations at your site. In off-site calibration, your instruments are sent to the provider’s laboratory for calibration.
Opt for off-site calibration for:
- Bulk calibration of a large number and/or variety of instruments
- Special cases where the calibration requires special equipment or procedures
- Instruments whose downtime isn’t that critical to your current projects
However, it has some disadvantages:
- Possibility of equipment damage while in transit
- Logistical challenges and relatively longer downtime
- Additional costs for logistics, shipping, and equipment insurance
In all other cases, opt for on-site calibration which minimizes your instrument’s downtime.
Look to Keysight for Your Calibration Services
In this article, you got an overview of calibration services and the knowledge needed to select a reliable calibration vendor. At Keysight, we offer comprehensive calibration services for all your needs — and not just for Keysight products.
We also calibrate these instruments from Tektronix, Rohde & Schwarz, Anritsu, National Instruments, Fluke, Keithley Instruments, Teledyne LeCroy, General Radio, Mettler Toledo, Wavetek, and more:
- Oscilloscopes and signal analyzers
- Multimeters, data loggers, and recorders
- Signal generators, function generators, and power supplies
- Micrometers, calipers, tachometers, thermometers, thermocouples, torque wrenches, and many more
In fact, we have expertise in calibrating and adjusting a wide range of parameters — dimensional, optical, electrical, electro-optical, and physical — for many different types of measurement equipment.
Our worldwide facilities areaccredited by national accreditation bodies. We offer multiple levels of calibration services to suit your quality, project, or budget requirements.
Standards lab certification carries the highest assurance of quality with traceability to a primary or NMI reference standard.
In every offering, we include all details of performance and adjustments in our reports. All reports and calibration certificates are accessible 24×7 via our KeysightSupport Portal.
Start your calibration with us by selecting ourcalibration services, or contact us for your special calibration needs!