How Do I Read a Calibration Certificate?

A year has gone by already, you’ve had your equipment calibrated, and great news – it passed! You can rest assured that your instrument readings are accurate and reliable for at least another 12 months. But they’ve sent you a document – your  multimeter calibration certificate –  it’s full of numbers, symbols and unfamiliar logos and you wondering “How Do I Read a Calibration Certificate?” It must be important, as they’ve told you to keep a copy in case it is requested in an audit or even by a customer. So, what does it all mean and why do you need it…?

In this post – whether you’re a Calibration Technician, Equipment Engineer, QA Manager, or an independent tradesman – we will share with you the importance of your newly acquired document, and how you can decipher it fully.

What is a Multimeter Calibration Certificate?

Also known as a calibration report, the definition of a calibration certificate could be surmised as a record of the results taken in a calibration test on a specific single instrument. The test will have been carried out, and a certificate issued by an accredited calibration laboratory, who will offer full traceability in the document to prove the confidence in the readings. 

Why do I need a Calibration Certificate?

It may be required in a Quality Assurance (QA) Audit, or in some cases it may be called upon to verify other equipment it is associated with, potentially years down the line. The certificate should be filed, ideally in a digital format, or physically with paper copies and kept as evidence that the equipment is performing as it should be. The calibration laboratory will keep a copy too for the same reason. but before knowing why you need a certificate, you need to answer “How do i read a calibration certificate?”, continue reading to learn more. 

How do I read a Calibration Certificate?

Your multimeter calibration certificate should be clear and easy to read. Ideally spanning a single page, this enables you to display the certificate if required but also so you can see all the information at a single glance, rather than rifling through pages and pages of detail. 

Whether it is a multimeter calibration certificate you have in front of you or a digital pressure gauge calibration certificate, the backbone of the calibration certificate format should remain the same.

Below is an example of a GNW Instrumentation calibration certificate, and we will guide you through how this information is applicable using a key.

A – Lab Name

The issuing calibration laboratory’s name

BLab Address

C – Lab Contact Details

DNational Standard and Auditer Logos 

Official logos proving the Lab’s strict compliance – the only National Standard, ISO 9001 and their Independent Auditer

E – Cert No

Unique certificate number allocated by the laboratory


A brief description of the instrument being tested


The company the instrument was originally made by

HSerial No

Sometimes called an ‘asset number’, this number remains with the instrument indefinitely to safeguard full traceability. Sometimes it can be allocated by the lab when no number is present on the instrument itself

I – Range

The lowest and highest capacity the instrument can provide

J –  Customer

The name and correspondence address of the company that has requested the calibration

K – Date of Calibration

The date the calibration was carried out

LTest Equipment Used

Details of the Lab’s test equipment used referenced by a Unique Internal Procedure Number (UIPN)

MTest Increments In 

The unit the instrument measures in e.g., kg, psi, mBar


The smallest increment that can be read on the instrument

OBarometric Pressure

The atmospheric pressure on the date of calibration, which can affect the outcome of calibration readings


the percentage of water vapour in the air on the date of calibration, which can affect the outcome of calibration readings

QApplied Test Value

The reading the instrument capacity was targeted towards using the Test Equipment (L)

RActual Reading as Found

The reading the instrument provided

SActual Error as Found

The difference between the two readings in (Q) and (R), shown as both plus (+) or minus (-) to avoid misinterpretation 

TAdjustment Statement

Statement confirming the instrument is measuring within the correct tolerances. Where necessary, an instrument may be adjusted to correct its readings, in which case both the before adjustment and after adjustment readings will be reported

UInstrument Status

A clear ‘PASS’ or ‘FAIL’, determined by the numerical results of the test and its tolerances. In the instance of the latter, the customer will be informed, and they can decide whether they choose to have the instrument repaired and recalibrated, or Quarantined to remove it from service

V – Uncertainty Statement

Despite the best equipment and best-controlled environments, there is always some variation in measurements. An uncertainty value is based on a variety of factors, such as repeatability, linearity, atmosphere, equipment, etc., to present a figure that covers them all. By measuring the uncertainty, you can be even more confident in your results. 

WAuthorised Signature

The signature of the approved representative from the issuing laboratory

How can I verify a Calibration Certificate?

Ok. so we have answered the original question of “how do i read a calibration certificate?” but now you need to how to verify one. If you have received a Calibration Certificate, or it has come into your possession, you can verify its authenticity through either the Issuing Laboratory or their Independent QA auditor who can verify it on your behalf. The Auditor ensures that the Issuing Laboratory complies with the rigorous procedures of the National Standard, ISO 9001 on an annual basis, so you can be confident the calibration was carried out to an exacting method.

Where can I get a Calibration Certificate?

Every instrument that is calibrated by GNW Instrumentation is issued with a Calibration Certificate as standard. We can provide digital or paper copies if preferred, and by request can even compile these onto an External Hard Drive or CD Rom if required. Like most documents created by a business, copies of all certificates are kept for six years after they expire as outlined by Section 5 of the Limitations Act 1980. 

If you are an Asset Manager responsible for hundreds or thousands of instruments for your business, GNW Instrumentation also offers the option to utilise a custom-built ‘Instrument Tracker’, a personalised client portal with a unique log in enabling all verified users to access the calibration history and certificates at any time. It also works on a phone or tablet!

In conclusion, a calibration certificate is a valuable piece of your calibration puzzle – without it you cannot be assured your equipment is working accurately and consistently. We hope this has gone some way in answering the question “how do i read a calibration certificate?”. You can read more about why your company needs a calibration certificate in another one of our latest blogs

To make sure you are getting the best out of your calibration certificate, you need to:

  • Ensure your certificate has everything it should (see the above example). 
  • Devise an easy-to-use filing system, preferably a digital one

TIP! Use GNW’s Instrument Tracker Portal and we will do it for you.

  • Set timely reminders a few weeks before the calibration expiry date – but GNW will contact you automatically.
  • Calibration should be performed no less than once a year, every 6 months if it is used more frequently or is portable. A lot can happen in that time, including damage!
  • GNW will provide a fully traceable test certificate compliant with the National Standard ISO 9001.