5 Mistakes When Using a Calibration Certificate that You Need to Correct

with 14 Comments

During my time as a calibration engineer managing an in-house calibration lab, I have collected different types of calibration certificates coming from different users inside the company. I observed that each certificate has different formats and contents.

And one day, one of the calibration certificates we have gives us a non-conformance because it is not an accredited certificate or not from an accredited calibration lab. The company I belong at that time is manufacturing semiconductors (IC) for automotive where an accredited lab is a requirement.

Have you ever encountered the same problems regarding the use of your calibration certificates? How do you review a calibration certificate and document the most important details that suit your requirements?

In this post, I have presented:

  1. What is the purpose of a calibration certificate,
  2. Why there are different content of a calibration certificate?
  3. 3 types of calibration certificates that you need to be aware of.
  4. What are the advantages of having an accredited calibration certificate?
  5. 5 mistakes when using a calibration certificate

What is the Purpose of a Calibration Certificate?

The question above is very simple which has also a very simple answer (in which it is). The simple and very basic answer is to show that a specific instrument is calibrated and within a calibration period.

But if you truly understand the content of a calibration certificate, you will realize that it is not a simple question.

In order to fully benefit the importance of calibration certificate and if you are making measurements regularly using the calibrated instrument, you should always consult the calibration certificate for the following:

  1. The error and correction factor
  2. The uncertainty results
  3. As-found and As-left data
  4. The tolerance
  5. Traceability evidence

And if you are monitoring quality and compliance, you should review the following:

  1. Calibration interval
  2. As-found and as-left
  3. Written remarks
  4. Traceability information
  5. Details like correct information
  6. Compliance to specifications

Check out the related post in this link>How to read a calibration certificate

Why Are Calibration Certificates Have  Different Contents?

Many users are not aware of the different types of calibration certificates until they are audited and have a non-conformance.

Calibration labs have different calibration certificate formats or content for some reasons. These reasons are:

  1. They are not an accredited calibration lab and therefore does not follow the ISO 17025 calibration certificate requirements. See the requirements here
  2. The lab is following a customer requirement on what to reflect only in the calibration certificates as per their application.
  3. Other labs are following different formats and requirements as per the standard they are using like ANSI/NCSL Z540 in the US.
  4. Some other reasons which are related to the cost of calibration are to reduce the calibration price and at the same time limiting the test points and other information on the calibration certificate.

To prevent or avoid any problems, make sure to:

  1. Be aware of the different types of calibration certificates that you will receive and use,
  2. Familiarize yourself with the calibration certificate requirements as per ISO 17025:2017,
  3. Determine your requirements and internal policy or procedure regarding what you want to be displayed in your certificates by 3rd party calibration lab,
  4. and as much as possible, get the service only to an accredited laboratory under ISO 17025.

3 Types of Calibration Certificates That You Need To Be Aware Of.

Being aware of the different types of calibration certificates will immediately prompt you to take immediate action once you notice a different format of the calibration certificate you receive. Therefore, a review of the calibration certificate after receipt is important.

If you are not aware of this and you receive their certificate, this will become a potential problem for you during audits.

To prevent this, I will share below different types of calibration certificates:

1. Accredited calibration certificates – this certificate follows the format of ISO 17025 requirements and it is the required calibration certificates if the lab is accredited under ISO 17025.  Check this link to view the full requirements

Accredited Certificate with accreditation body logo

          The main difference that is included here are:

  • The LOGO of the accreditation body
  • The  measurement uncertainty results
  • The statement of conformity with requirements or specification
  • Results of before and after adjustments or repair
  • Opinions and Interpretations if applicable
  • Traceability Information

Plus all the contents of other calibration certificates are included here, if applicable and required by the user.

2. Non-Accredited Calibration Certificates – as the name implies, this is the calibration certificates provided by a lab that is not accredited under ISO 17025. And therefore does not follow its requirements.

Original Equipment Manufacturer Calibration Certificate
  • You will easily determine that a calibration certificate is not accredited under ISO 17025 even though they follow its format if there is no LOGO of the accreditation body.
  • This type of certificate is used by the Original Equipment Manufacturer, also known as a Traceable calibration certificate. They use this for the instruments they manufacture. Most OEM certificates have less information compared to an accredited certificate.

3. Conformance  Certificate– this type of certificate has limited or no measurement data results. It only details specific information and the functionality of the instruments and certifying that the instruments have passed or meets the quality check on product performance.

  • This is mostly used by OEM for certifying the quality of a batch produced instruments.
  • You do not need this type of certificate if your purpose is in the accuracy of measurement results because it will not show the performance of the instruments and therefore it is not a valid calibration report.
Conformance Certificate

For more details you may check these articles:

Fluke Calibration Certificates

Types of  calibration certificates

What are the Advantages of an Accredited Calibration Certificate?

As we can see, there are different types of calibration certificates that we need to be aware of. Below are some of the reasons why we need to use or have an accredited calibration certificate:

  1. It has uncertainty results that you can use for your in-house calibration lab.
  2. There is a high assurance that the calibration results are properly checked and monitored since technical competence is verified during the accreditation.
  3. Traceability to National or International Standards is assured which is one of the main requirements of ISO9001:2015 calibration requirements under clause
  4. With the calibration certificate, format/content stated under ISO 17025 will ensure that customer requirements (and auditor’s requirements) are met.
  5. Customer support is highly expected when problems arise involving the calibration results.

5 Mistakes When Using a Calibration Certificate

Most users that I observed only use the calibration certificate to record the calibration date and due date. Another is just a  “show-off” for the auditor in case they will ask for its calibration details. Certificates are used as a “display” only.

This is a mistake because we are not using the full importance that will provide greater benefits, we are just displaying a calibration certificate. As often as possible during measurement, you should review and analyze its content.

Moreover, If you are implementing ISO 9001:2015, this could be a potential non-conformance because you neglect to implement its requirements to analyze and evaluate the measuring instruments used. This is a requirement under clause 9, Performance Evaluation, with sub-clause 9.1.1 which states that:

The organization shall determine:
b) the methods for monitoring, measurement, analysis, and evaluation needed to ensure valid results;
d) when the results from monitoring and measurement shall be analyzed and evaluated.

My exposure in an in-house and 3rd party calibration lab leads me to observe and encounter below 5 mistakes when using a calibration certificate.

1. Not reviewing the specific information once received
. A review of calibration certificates should be included in the procedure regarding 3rd party calibration.  

  • This will ensure that the correct details reflected in the calibration certificate. Wrong information like the “serial number” will invalidate the traceability of the calibrated instruments on its certificate.
  • Check for the traceability information – this is one of the main requirements of ISO 9001:2015 as stated under the advantages above. I have a read a good article which shows different formats and traceability statements in a calibration certificate.. measurement traceability
  • Other information that needs to be reviewed like the calibration results- Check my other post here.

2. Not using the correction factor.

  • Most of the results of the instruments that are calibrated and cannot be adjusted have a correction factor (CF) with it. This must be used every time you are making a measurement to compensate for the error.

To compute for the Correction Factor:
CF = true value-actual value

Check my other post which I explained this in more detail in this link.. correction factor

3. Neglecting to review the remarks.
This one is critical, in any case, that the instruments have a problem during the initial calibration, we can isolate immediately and perform assessments to the affected products where the instrument is used.

These remarks that we need to be aware of includes:

  • out-of-tolerance or failed
  • a limited calibration – not all range is covered during calibration.
  • Other important information that the lab wants you to know about the performance of the calibrated instrument, an example is “current function is defective”.
sample remarks

4. Not comparing the previous results from the latest
This is one of the requirements under ISO 9001 clause which states that “The organization shall determine if the validity of previous measurement results has been adversely affected when measuring equipment is found to be unfit for its intended purpose, and shall take appropriate action as necessary”.

We will check here the “As found Data”  which is the result of calibration before any adjustment with the “As Left Data”, which is the result after the adjustment.

The benefits of recording and reviewing the data results are:

  1. Comparing this data will show you if there is out of tolerance found before the adjustment takes place.
  2. the long term trend can be seen and the performance of our instruments will be determined. You will observe here if it is going near the limits or readings are still stable.
  3. By recording the performance, this will show you if you need to adjust the calibration interval of your instruments. This is valid evidence when you plan to extend the calibration interval of your instrument. How to implement this? Check out my other post in this link>> calibration interval adjustment procedure

5. Using a calibration certificate that is not issued by an ISO 17025 accredited laboratory.
There is an instance when there is no available calibration lab that is accredited under ISO 17025  to calibrate our instrument. Where the only options are:

  • To have it calibrated by a non-ISO 17025 accredited lab, or
  • To send it back to the Original Equipment Manufacturer (OEM) (most OEM are not ISO 17025 accredited).

Please don’t get me wrong here, it is not a mistake to use a calibration lab that is not accredited under ISO 17025, actually if you are following ISO 9001, the only requirements is to use a calibration lab with “measurement standards traceable to International or National measurement standards”.

But this will become a mistake if you are not aware of the requirements of your internal procedure or the certification bodies you applied for.

Most certification bodies have a policy regarding calibration service providers where  “it should be ISO 17025 accredited”, with this requirement, mistakes or non-conformance will occur unless the below are implemented:

  • There should be evidence that the user has searched for an ISO 17025 accredited lab and none where found.
  • There should be evidence that the chosen lab has sufficient capabilities and traceability to meet your requirements.

Check this article for more details>>calibration certificate content


A simple calibration certificate as we see can be a source of non-compliance or a process problem if not given time to understand and interpret the content. In this post, I have presented this article in order to help and guide us for some requirements and formats that we need to be aware of when required to review and use a calibration certificate.

I presented the following:

  1. What is the purpose of a calibration certificate,
  2. Why there are different content of a calibration certificate?
  3. 3 types of calibration certificates that you need to be aware of.
  4. What are the advantages of having an accredited calibration certificate?
  5. 5 mistakes when using a calibration certificate

I also included in this post the related clause for Performance Evaluation under ISO9001:2015 which is related to calibration implementation.

Thank you for reading my post, please comment and subscribe.

You can also connect with me on my Facebook page


14 Responses

  1. Sonny D
    | Reply


    I noticed Calibration Certificate recommends a 12 month calibration interval. It is difficult to understand the logic behind the 12 month interval, shouldn’t this depends on the number of usages ? It is probably making more sense with say a 12 month interval or 500 uses (ie. instrument uses 2 times/day for 52 weeks) recommendation, whichever comes first. This kind of recommendation makes life easier for management to budget funding. What is your thought on this subject? Thanks.

    Sonny D

    • Hi Mr. Sonny,
      Thank you for reading my post.
      Actually, as per ISO 17025 standard, it is not allowed to put a calibration due date in calibration certificates if unless communicated and agreed with the customer.
      This is also the reason why it is stated as” recommended “due date, not the actual due date.

      Most due dates are based on:
      1. Experience on the same type of instruments
      2. Manufacturer recommendation
      3. Calibration Laboratory recommendation

      You are correct; it depends on the number of usages the owner has acquired or how frequent it is being used. You should be implementing the best calibration interval that gives more sense to you as the tool owner.

      You can put in your procedure that, in every 500 uses, you will have it calibrated. And after 3 times in a row where the instrument is calibrated, and as you record and track the performance, you observe that it is still within limits or very stable, you can decide and increase it to 1000 uses before having it calibrated again. This is now your new calibration interval. This is just an example but it can be implemented in this principle.

      Hope this helps.

      • Christopher Rodil
        | Reply

        Helo Sony and Edwin,
        Good day to both of you! Since the topic when the instrument to be calibrated? For me its depend upon to the criticaly of the instrument in terms of usage. In my last plant which is the process is food, diff variety of instrument with diff freq of calibration..we clasify our instrument in CP-critical point (3months), CCP critical control point, (1 month)and MO – monitoring only ( 1 year). we follow QMS FSMS because the product is food the instrument is more frequent to be calibrated..
        Assuming new instrument brought in calibration workshop for recalibration and enroll in CMMS and we dont know what to put calib freq and the vendor also dont care..as per ISO recommendation and manufacturer, 1 year is the best frequency for recalibrating the instrument but its depend also the company whether the budget is tight to lessen the calibration of their instrument or to avoid downtimes interms instrument failure..Big companies probably comply this but fly-by-night? I dont think so..I hope I contribute small topic to be discuss..

        Chris Rodil

        • Hi Christopher,

          Thank you for sharing your thought and experience in this topic. You have contributed good information that each of us can learn and adapt. Classifying an instrument based on its criticality in usage is a good way to determine what calibration interval you can use. It is really very important that we need to assess properly how we used our instruments in order to come up with a good calibration interval.

          I appreciate your time sharing this.

          Best regards,

  2. Ong Zheng Da
    | Reply

    Hi Edwin,

    Would like to seek your advise regarding reporting of options calibration result such as laser and touch probe. For iso 17025 accredited calibration report, if customer has calibrated laser and touch probe, is it necessary to input the results in a separate category together with xyz results and uncertainty calculation? And also does laser and touch probe require separate scope of accreditation in order to justify calibrated results?

    Thank you
    Best regards
    Ong Zheng Da

    • Hi Ong Zheng Da,
      Good day!

      There are no standard formats in displaying results in a calibration certificates as long as the requirements are followed.
      With your concern, yes, it can be in a separate category if it can show more clarity to the user.

      As per my structure, I will put all the measurement results on the same page if it can accommodate all.

      With regards to laser and touch probe if it needs a separate scope, yes, if this is a separate category or services.

      But as per my experience, laser and touch probe does not provide direct measurement results, they are part of the system as a tool. The calibration part is more on alignment or positioning or other functions that are not considered as measurement, which falls under equipment maintenance. If this is the case, you do not need to include in the report if the customer does not require it, but make sure you have the data just in case requested. I may be wrong with this but you must verify with your Engineers.

      What I can suggest is that, since laser and probe are part of the measuring equipment, if there is a significant error contribution that you cannot remove (through adjustment), you just need to determine the error contribution and include it in the uncertainty budget.

      I hope this helps,

      Thanks again for reading my posts.


  3. Fred Mac
    | Reply

    Hello Sir,

    Good day.
    My question is, if there is no available ISO 17025 accredited lab to perform calibration on my unit (not Covered by their scope of Calibration.
    ie. Partial Discharge test, Is it acceptable to have it calibrated by OEM that is not ISO 17025 but SO 9001:2015 certified.


    • Hi Fred,
      Good day!

      Yes, correct. But make sure you have the record to prove that you have searched for an accredited lab. OEM are the most competent to calibrate their instrument therefore they are accepted.
      Ensure also that you performed supplier evaluation where you confirmed their traceability and competency of personnel involved.
      All these records can be asked during an audit.

      I hope this helps,


  4. nora
    | Reply

    Hello sir,
    We run lab to test energy meter with ISO 17025. How to deside the conformity statement.

    • Hi Nora,
      Before you can decide conformity for every instruments, you need to know what is your tolerance limit and the measurement uncertainty results. The way you use the uncertainty results will lead to your conformity statement. There are different ways on how to do this, I have created a separate post for this. Please check this link>> decision rule

      I hope this helps,

  5. Dear Edwin,
    Please, which better form for issued calibration report:
    – Calibration certificate OR Certificate of calibration.
    With thanks

    • Dear Sir,
      Either one of them is ok but I prefer ‘calibration certificate’, this is the most known format or name that a customer understands most in my opinion.

      Thanks and regards,

  6. Alana
    | Reply

    Hello, I was wondering who can write up a calibration certificate.. and if you have to be accredited to anything to be able to do so?

    • Hi Alana,
      Anyone that has a training in calibration and understanding of the requirements of Standards ( ISO 9001 or ISO 17025) can write up a calibration certificate. It is not necessary to be accredited, as long as you follow the requirements, specifically the requirements under ISO 17025 standards, you are good to go with your certificates.
      The important thing here is that the certificate is approved and controlled under Control of Documents by the quality department.

      I hope this helps,

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.