Calibration FAQ

Calibration FAQ

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Calibration refers to measuring, with the instrument in question being calibrated or tested against a known source.
Certification is what is granted after calibration. It is a document which confirms the accuracy of the instrument by showing the results of the calibration exercise.

A calibration certificate is an official document to show that your thermometer has undergone a calibration test in an accredited laboratory. The test date, method and results are shown on the certificate.

The calibration test compares your thermometer measurements with a traceable device or reference thermometer.

This documentation proves the accuracy of your thermometer. If the results show that the thermometer is inaccurate, it will need recalibrating. You will receive fresh documentation to show this.

Calibration certificates are not a legal requirement in the UK. Within catering applications, your HACCP plan will determine how and when your business should calibrate your thermometers.

However, a calibration certificate is the only legal document that proves your equipment is accurate. There are several benefits to this:

A calibration certificate can be used in court if a health and safety issue relating to unsafe temperature occurs.
Calibration certificates are useful for EHO visits and other inspections or audits.
Ensuring your thermometers are calibrated to a high level of accuracy will preserve the quality and safety of your temperature checks.

ETI can issue UKAS certificates for temperature and humidity data-loggers with internal or external probes. The standard certificate includes three different temperature or humidity points, but we can issue certificates covering anywhere from one to five points.

The more regularly your thermometers and measuring devices are calibrated and certified, the more assured you will be of their accuracy. We recommended you obtain a certificate at least every 12 months.

Yes. ETI sells a large range of calibration equipment and accessories. These include reference thermometers that are ideal for comparison checking the calibration and accuracy of other thermometers and probes, when used in conjunction with a stable temperature heat or chill source.

However, conducting calibration activities yourself may not be as accurate or provide as certain results as sending off your instruments to a UKAS certified laboratory.


We pride ourselves on providing a quick and efficient service – ETI typically completes calibration and certification within 10-14 working days, Humidity Calibration up to 20 days.  


As with any measuring or calibration activity, there will always be a probability of inaccuracy due to equipment or human error, or inconducive testing environments. Each measurement therefore has an uncertainty factor which is stated as a tolerance of plus or minus the measured figures. ETI’s laboratory offers certified uncertainties from ±0.02°C.

UKAS Laboratory FAQ

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The United Kingdom Accreditation Service (UKAS) is the United Kingdom’s lone National Accreditation Body. Mandated by the government, its responsible for the assessment of organisations that provide conformity assessment services such as certification, testing, inspection, calibration and verification against national and international standards.

It is Government policy to recommend the use of UKAS accredited conformity assessment services whenever this is an option. UKAS essentially ‘checks the checkers’. Indeed, those that achieve UKAS accreditation have demonstrated their competency, impartiality and performance capability as an evaluating party. 

Source: UKAS

ETI currently holds ISO 9001:2015 Quality Management System (accredited by BSI), and ISO 17025:2017 Temperature and Humidity (accredited by UKAS).

Whilst we are not accredited to any HSE ISO standards specifically, we have a Nebosh qualified Health and Safety officer and experience safety team actively encouraging safe practices. This team is also responsible for monitoring our environmental impact and obligations under WEE and Waste Battery regulations.


UKAS ISO 17025 accreditation is the single most important standard for calibration and testing laboratories around the world. Being an ISO 17025 accredited laboratory demonstrates that we are technically proficient and able to produce precise and accurate test and calibration data. This goes hand in hand with research and development when creating and producing a new product, as it enables us to gain accurate and consistent production level calibrations on every single thermometer produced by ETI.

This is a continual exercise. Critical equipment is routinely checked in house using international standards such as gallium, triple of water and other fixed cells to ensure its reliability, with equipment of greater importance checked more frequently. There is also necessary auditing and training exercises to ensure adherence to the laboratory standard (17025:2017). Part of being an accredited laboratory is having clear documentation showing that this maintenance takes place and how it is then put into action.

One of the biggest changes we have made was investing in more temperature baths. This has allowed us to better manage the quantity of work we are now receiving, as well as granting us more flexibility when carrying out work at points that differ from our usual standard five.

Another aspect we worked on is being able to deliver a better uncertainty of measurement with our lower range of temperature (down to -80°C), as we now have more space to work. Simply we were able to invest in better equipment to carry out the work we were already doing.


When a thermometer undergoes calibration, its readings are checked against a reference thermometer. The reference thermometer must have already had a calibration test using an even higher standard than the one currently being done.

Every time a device has a calibration test using a thermometer that has been calibrated to a higher standard, it forms a chain. When this chain is unbroken and leads back to the highest-level reference thermometer in a national calibration centre (or equivalent) it becomes traceable.

A traceable certificate means that your thermometer has been tested against a reference thermometer within the traceability chain. This is often satisfactory for EHOs and other inspectors who may want to check your calibration procedures during visits.

A UKAS certificate means that your thermometer has been tested in a UKAS accredited laboratory. This will give you additional peace of mind that your thermometer has been calibrated using the highest standards within the UK.

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