Measurement devices: How to avoid audit issues

Manufacturers must fulfill the regulatory and standardized requirements for measurement devices.

The measurement devices are part of most audits (ISO 9001, ISO 13485) and inspections (see 21 CFR part 820). This article introduces these requirements to you and shows you how to fulfill them.

In addition, the article will explain where the differences between “gauging”, “adjustment”, “verification” and “calibration” are found. You should know these differences to be able to really understand the regulatory requirements to fulfill them and avoid problems during an audit.



“Please note: This article is about measurement equipment and measurement devices, not medical devices with a measurement function.”

1. Definition of terms

In colloquial language, we use terms such as “adjustment” and “calibration” sometimes as synonyms and often differently from the standards. In order to understand and fulfill the regulatory requirements, manufacturers must know and master the definition of terms.

a) Calibration

Based on DIN 1319-, calibration means the comparison of the measurement or expected value with the true or correct value. This means that the measurement device is not changed during calibration!

You'll note: Colloquially, one often uses the term calibration differently.

In calibration, one often uses a measurement standard that can be traced back in a calibration chain to the national standards of the physical-technical Federal Supervisory Board PTB.

b) Adjustment

What is meant colloquially by calibration, is actually adjustment, meaning that the setting or alignment of a measurement device to minimize a systematic measurement deviation as much as possible.

c) Gauging

Gauging can and must only be done to measurement devices where legally required. This is typically the case if there is a safety-critical or public interest (meaning that money flows like the pump system of a service station).

So with gauging is the testing and stamping of a measurement device according to the gauging requirements done by the responsible gauging authorities. In other words: Gauging is a test of whether a measurement device meets the legal requirements, such as the Weights and Measures Act or Gauging Ordinance.

In addition: Measurement devices that must be gauged, must only be brought to market after a conformity evaluation procedure according to the  Weights and Measures Act (MessEG).

d) Measurement equipment and measurement devices

DIN 1319-2 defines measurement equipment as a measurement device, measurement system, a standard, a resource or reference material that is needed to perform a task in measurement technology. Measurement equipment for testing are also called test equipment.

The regulatory requirements mention measurement equipment, but usually mean measurement devices.

2. Regulatory requirements for measurement equipment/measurement devices

a) Requirements of ISO 13485

ISO 13485:2016 addresses requirements for handling measurement equipment in multiple chapters.

In chapter 7.5.1, the standard requires that the manufacturer regulate “Monitoring and Measurement Equipment”.

The standards clearly explain “Regulation of Monitoring and Measurement Equipment” in chapter 7.6. It obligates the manufacturer to:

  • Calibrate measurement equipment, adjust it if needed and document this,

  • Ensure that the measurement devices remain calibrated and

  • that all procedures are documented and observed.

b) Requirements of 21 CFR part 820 (Quality System Regulation of the FDA)

Very similar requirements are set by the FDA in 21 CFR part 820.72(“inspection, measuring, and test equipment“).

This administrative law also requires the regulation including calibration, adjustment and documentation of the measurement equipment according to set procedures. Here too, the manufacturers must set the accuracy requirements and take measures if it is found retroactively that these were not fulfilled.

The recordings should show who performed which test (calibration) with which results and when the next test is pending.

3. Tips for fulfilling the regulatory requirements

a) “Inventory List”

Manufacturers should absolutely keep a list of all measurement equipment. If necessary, various company departments can keep their own lists. These list(s) should describe the measurement devices with:

  • Clear identification, such as ID or device number

  • Name and/or model and manufacturer of the measurement device

  • Type of device (e.g. voltmeter, ultrasound device for density measurements)

  • Reference to the device card (file, database entry, physical storage location)

  • Person or organizational unit responsible for the measurement device and updating the device card

  • External persons or organization responsible for the calibration, adjustment and possible gauging

b) Device Card

A “Device Card” (paper, electronic file) must exist for each measurement device. This contains the aforementioned attributes as master data. In addition, it describes:

  • Location and/or process / work step in which the measurement device is used

  • Device specific specifications for testing, calibrating and gauging the product. This includes the intervals and responsibilities for the work steps.

  • History of work steps and results

    • Date

    • Person

    • Activity, e.g. calibration, adjustment, commissioning

    • Results

    • Device status (approved, blocked)

For some companies it has been beneficial to integrate the list of all measurement devices into the list of all tools.

Additional information

“Please also see the detailed description of the requirements on the validation of tools.”

c) Process instructions

Whether a manufacturer requires one or more process instructions also depends on how heterogenic the measurement devices are. The process instructions could regulate, for example:

  • Who updates the inventory list, how often and in which form

  • Which device-specific information the Device Card contains and in which form this must be documented

  • Which training of the process instructions must occur and how often

  • Who checks whether the process instructions have been followed and how often

  • How the requirements of ISO 13485 for the regulation of recordings are fulfilled

Special case (stand-alone) Software


There is stand-alone software that one considers the standards for measurement equipment, such as:

  • Tools for static code analysis

  • Test suites to automatically implement and analyze unit tests

  • Software for image analysis, as they are used in the final testing

However, software is also often part of measurement equipment. One example is a system that analyzes sensor signals in production and decides whether the part produced or (medical) device meets the specifications.

Implementing regulatory requirements

ISO 13485 requires the calibration or verification of the measurement equipment. For software, there is usually no comparison to a standard. Therefore, the test of the measurement equipment takes place in the form of a verification. Details on this can also be found in the mentioned article on validation of tools.

There also cannot be a gauging of software, because there are no legal requirements for this.

An adjustment could also be necessary if software was incorrectly parametrized or configured.

For software that is part of a measurement device, the manufacturer must also fulfil the requirements for “Computerized System Validation”.

Additional information

“Read more on the topic here Computerized Systems Validation (CSV).”

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