When a torque wrench, torque transducer or pressure gauge returns from calibration, the value of the certificate depends on more than the results printed on the page. The method used to obtain those results is equally important. Internationally and nationally recognised calibration procedures give laboratories a documented and repeatable way to perform the work, helping customers understand what was measured and how the results should be used.
This does not mean that one procedure suits every instrument. The appropriate method depends on the equipment type, measurement range, operating mode, intended application and the customer’s requirements. The important point is that the laboratory selects a technically suitable procedure and applies it consistently.
What are recognised calibration procedures?
A calibration procedure describes how an instrument is compared with suitable reference equipment. Depending on the measurement and the applicable standard, it may specify:
- how the instrument is identified, mounted and prepared;
- the reference equipment to be used;
- environmental conditions that need to be controlled or recorded;
- preloading, exercising or stabilisation requirements;
- the number and location of measurement points;
- the direction and sequence in which loads are applied;
- the number of repeated readings;
- the calculations used to determine results;
- how measurement uncertainty is evaluated; and
- the information to be reported on the certificate.
A recognised procedure may be published by an international standards organisation, a national standards body or a technically established industry organisation. It provides a common reference point for the laboratory and its customer.
The procedure should always be identified by its correct title, number and revision where applicable. Simply writing “calibrated to an international standard” is not enough for a customer to determine what work was actually performed.
Why recognised calibration procedures matter
They improve consistency
A written procedure reduces the risk of important steps changing between technicians, instruments or calibration dates. It establishes the order of the work, the required measurement points and the way results are calculated and recorded.
This consistency is particularly valuable for equipment used in manufacturing and maintenance. If a torque tool is used to control an assembly process, the customer needs confidence that each calibration is performed on a comparable basis. Otherwise, changes in the method could be mistaken for changes in the tool.
Consistency does not mean every laboratory will obtain exactly the same result. Differences can still arise from the instrument’s behaviour, environmental conditions, reference equipment and measurement uncertainty. A recognised procedure provides the structure needed to investigate and interpret those differences.
They produce results that are relevant to the application
A technically correct measurement can still be of limited value if it does not cover the way the instrument is used. For example, a torque tool may be used in both clockwise and anticlockwise directions, or only across a particular part of its operating range. A calibration that covers the wrong direction or unsuitable test points may not provide the evidence the customer needs.
Recognised calibration procedures help define the item type, operating mode, range, direction, units and loading sequence. This makes it easier for the laboratory and customer to agree on suitable work before calibration begins.
They provide a sound basis for measurement uncertainty
Every calibration result has measurement uncertainty. This is the quantified doubt associated with the result; it is not an admission that the result is wrong.
Depending on the equipment, uncertainty can be influenced by:
- the reference standard;
- repeatability of the readings;
- display resolution;
- alignment and mounting;
- loading characteristics;
- temperature and other environmental conditions; and
- the behaviour of the instrument during the measurement sequence.
A recognised procedure helps ensure that the important influences are considered in a consistent way. The laboratory must still evaluate its own equipment and method implementation, but the published procedure provides the technical framework.
They make records easier to understand
Calibration certificates are often reviewed months or years after the work was performed. They may be needed during an audit, an equipment investigation, a quality review or an assessment of previously completed work.
When the certificate identifies a recognised procedure, the reader has a clearer basis for understanding:
- how the calibration was performed;
- which measurement points were covered;
- whether results relate to calibration or conformance testing;
- how uncertainty was treated; and
- whether the method was suitable for the instrument’s intended use.
Good records also make future calibrations easier to compare. If the same method and appropriate measurement points are used over time, developing changes in an instrument’s performance are easier to identify.
They support confidence across supply chains
Manufacturers, maintenance contractors and equipment owners often exchange calibration records with customers and suppliers. A clearly identified, widely understood procedure helps each party interpret the work without relying on a laboratory’s internal terminology.
This is valuable in industries such as automotive manufacturing, aerospace, construction, mining, rail, power generation and heavy maintenance, where the same measuring equipment can influence several stages of a job or production process.
The benefit is practical: fewer questions about what was tested, less uncertainty about whether the results are relevant and a clearer basis for accepting the equipment back into service.
Recognised calibration procedures used for torque equipment
Torque calibration provides a good example of why laboratories need to select the procedure carefully. Hand torque tools and torque measuring devices perform different functions, so they should not automatically be treated in the same way.
ISO 6789-1:2017 for hand torque tool conformance
ISO 6789-1:2017 covers requirements and methods for design conformance testing and quality conformance testing of hand torque tools. It also specifies minimum requirements for a declaration of conformance.
This is important because conformance testing is not simply another name for calibration. It assesses the tool against defined requirements and supports a declaration about whether those requirements have been met.
ISO 6789-2:2017 for hand torque tool calibration
ISO 6789-2:2017 covers calibration of hand torque tools and the determination of measurement uncertainty. It provides a more detailed approach when measured deviations and associated uncertainty are required.
The distinction between Parts 1 and 2 should be clear on the documentation. A declaration of conformance and a calibration certificate answer related but different questions.
BS 7882:2017 for torque measuring devices
BS 7882:2017 provides a method for calibrating and classifying torque measuring devices, including devices used when calibrating torque tools. It covers static torque measurement, calculation of results and classification of the device.
A torque transducer, analyser or calibration device should not automatically be treated as though it were a hand torque wrench. Using a procedure written for the correct equipment type produces more meaningful results and documentation.
International and national procedures are not competing choices
An international procedure is not automatically better for every application, and a national procedure is not automatically less rigorous. The correct choice is the procedure that suits the instrument and the purpose of the calibration.
An international standard may be useful when equipment or calibration records move between countries. A national standard may provide a well-established method for a particular type of equipment or reflect accepted practice within a specific market. Some national standards also adopt or align with international documents.
Before selecting a procedure, the laboratory should consider:
- the type and design of the instrument;
- the quantity being measured;
- the required range and units;
- the instrument’s direction or operating mode;
- manufacturer instructions;
- customer specifications;
- contractual or regulatory requirements; and
- how the results will be used.
The standard’s name is less important than whether its scope matches the work being performed.
Using a published procedure should also be described accurately. Following a recognised procedure does not, by itself, make a calibration accredited; procedure selection and accreditation are separate matters.
What if no published procedure is suitable?
Not every specialised instrument or application is covered perfectly by an international or national standard. In these cases, a laboratory may need to use an industry method, a manufacturer’s procedure, a customer-specified procedure or a properly developed internal method.
The method should still be documented and technically justified. Its important characteristics need to be validated or otherwise demonstrated as fit for the intended use. Any agreed departure from a published procedure should also be clearly recorded.
This prevents the use of recognised standards from becoming a box-ticking exercise. The objective is to obtain reliable and relevant measurement results, not to force an unsuitable instrument into a procedure that was designed for something else.
What should customers confirm before calibration?
Providing clear information at the start helps the laboratory choose the right procedure and avoids gaps in the final certificate. Customers should confirm:
- the equipment type and identification;
- the required measurement range;
- the units of measurement;
- clockwise, anticlockwise or both directions;
- the intended use of the equipment;
- any specified international, national or customer procedure;
- whether calibration, conformance testing or both are required;
- whether a statement of conformity is needed; and
- any special reporting or contractual requirements.
When reviewing the completed certificate, check that the procedure is identified, the required range and direction were covered, the results are clear and any adjustments or repairs are distinguished from the calibration itself.
Torque Lab’s torque wrench calibration information provides a useful starting point when planning work for hand torque tools.
Better procedures lead to better calibration decisions
Internationally and nationally recognised calibration procedures give laboratories and customers a common technical basis for the work. They improve consistency, clarify what was measured, support meaningful uncertainty evaluation and make calibration records easier to interpret across businesses and supply chains.
The most important decision is not choosing the standard with the most familiar name. It is selecting a procedure that fits the equipment, its intended use and the customer’s actual requirements—and then applying that procedure carefully and reporting the results clearly.
Contact us to discuss your calibration requirements.