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The 5 Most Common Calibration Errors You Should Avoid in MedTech

Updated: Feb 7

A quick search of the FDA warning letter database shows more than a dozen entries around 21 CFR 820.72.

Calibration is a well-understood topic, yet we often see issues around it.

Calibration is covered in ISO 13485:2016 under 7.6, Control of monitoring and measuring equipment, and in 21 CFR 820.72, Inspection, Measuring, and Test Equipment.

Warning letters often find similar issues around the topic of calibration; therefore, we want to discuss the 5 most common pitfalls you should avoid.

5 Calibration Pitfalls You Should Avoid in MedTech

This post talks about:

  • Why is Calibration Necessary in MedTech?

  • Calibration Error No. 1: The most obvious – No Calibration Procedure.

  • Calibration Error No. 2: Lack of specific information in the Calibration Procedure.

  • Calibration Error No. 3: Not doing what you are saying!

  • Calibration Error No. 4: No End-of-Life Calibration.

  • Calibration Error No. 5: No Good Records!

Before we begin talking about common calibration issues, let's start with a more fundamental question:

Why is Calibration Necessary in MedTech?

Just as musicians must tune their instrument to ensure accurate and consistent sound, measuring equipment must be calibrated to ensure accurate and consistent evaluation.

To produce medical devices, you use several measuring instruments (e.g., micrometers, calipers, tensile testers, etc.) to ensure your output follows requirements and is within specification limits.

Regular check-ups on these measuring devices are essential to guarantee correct information, avoid measuring mistakes and, consequently, faulty products.

Therefore, calibrating your equipment is vital and should be a standard procedure.

For this reason, ISO 13485 defines calibration requirements.

Unfortunately, in practice, these requirements are often not implemented as they should be.

Based on our experience and information from FDA Warning Letters, we have summarized the most common mistakes MedTech companies make regarding calibration.

Calibration Error No. 1: The most obvious – No Calibration Procedure.

ISO 13485:2016 mentions under 7.6:

“The organization shall document procedures to ensure that monitoring and measurement can be carried out and are carried out in a manner that is consistent with the monitoring and measurement requirements.”

Similarly, 21 CFR 820.72 states:

"Each manufacturer shall establish and maintain procedures to ensure that equipment is routinely calibrated…".

While this seems to be an easy harvest, warning letters show that companies often struggle with the correct implementation of calibration procedures.

Calibration Error No. 2: Lack of specific information in the Calibration Procedure.

While the FDA is clear about what the procedure content needs to cover, e.g., "specific directions and limits for accuracy and precision", other warning letters show that the absence of a procedure is an issue and, of course, its content.

Thus, a good number of warning letters address the lack of specific information in the procedure, e.g.:

  • What equipment needs maintenance, at what frequency?

  • Provisions for handling, preservation, and storage of equipment so that the accuracy and fitness for use are maintained.

  • Requirements for retrospective review, evaluation, or analysis of potentially affected product in situations where measuring equipment has been found to be outside the limits of acceptable calibration

Calibration Error No. 3: Not doing what you are saying!

It does not stop once you establish a procedure with the right content – now, you must do what you say. Several warning letters show that recalibrations have not been performed. While specialized tools might be helpful to track due dates, other free-of-charge solutions are available to ensure recalibrations are carried out on time.

Calibration Error No. 4: No End-of-Life Calibration.

Another mistake we often see is not performing an end-of-life calibration. After the very last measurement you performed with a device, you must recalibrate the device one last time, thus "end-of-life" calibration.

Less pricey measuring equipment, such as certain stopwatches, are often repurchased instead of recalibrated. While the repurchase is not the issue, the lack of recalibration of the old equipment certainly is. The following graph explains why:

MedTech End-of-Life Calibration

C0...calibration at the beginning of an equipment's life

C1…First recalibration shows that the timespan between the calibration at the beginning of an equipment's life, and the recalibration is fine

Cn...nth recalibration shows that the timespan between the first calibration and the nth recalibration is fine

In this case, the lack of Cn leads to a situation where you cannot prove that the timespan between C1 and the end of an equipment's life is fine.

For many, it seems counterintuitive to spend money on recalibrating the old device before taking it out of service. However, it is necessary to ensure all measurements have been correctly covered.

Figure 1 also helps to evaluate what an adequate frequency might be to calibrate equipment routinely. A shorter timespan between two calibration points bears less risk. When unsure how often equipment should be recalibrated, starting with shorter timespans and gradually increasing them over time (and knowledge) is better.

The MDSAP audit approach explains that,

“The initial the frequency with which measuring and test equipment is calibrated is usually based on the equipment manufacturer’s recommendations. As the medical device organization gains experience with the piece of equipment, the frequency of calibration and maintenance may be adjusted, based on a documented rationale”.

Calibration Error No. 5: No Good Records!

Calibration records are essential documents and shall be reviewed and assessed before archiving. 21 CFR 820.72 and the ISO 13485:2016 provide a list of information that shall be documented. Terms such as “as-found” or “as-left” are essential to understand and correctly interpret. The MDSAP audit approach also points out to review an assessment of the effect of the out-of-tolerance situation under reviewing records.

Conclusion: Calibration Errors in MedTech

In this blog post, we discussed a partial list of calibration errors.

It is based on common calibration errors we see in the field and should assist you in establishing better procedures and making better decisions.

Are you familiar with any other calibration errors and want to share them with our community? Feel free to contribute & let us know about them in the comments!

If you have specific questions about Calibration, send us a message at

PS: If you want to learn more about Quality- and Supplier Management in MedTech, check out our free learning resources at our SIFo Medical YouTube channel.


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