Main Operating Functions

Main operating function: What the IEC 62366 doesn’t define

I have updated the article on the main operating functions (eg taking the definition of the next edition of IEC 62366 into account) and consolidated various other articles on the same theme.

The IEC 62366 formulates requirements for the main operating functions of medical devices. Unfortunately, they do not define the term function and causes confusion. This article provides a definition and examples of medical products main operating functions.

Main operating functions

Definition of IEC 62366: 2007

The IEC 62366 defines the term main functions as follows:

"One either frequently used or with the safety of the medical device related function, which is connected to a user-interaction"

The term "function" does not define the norm. You will learn in this article:

  • what a function is
  • when a function is critical to safety and
  • when a function is often used.

Definition of IEC 62366: 2015

The next edition of IEC 62366 changes the definition of the main operating function:
function that involves USER interaction that is related to the SAFETY of the MEDICAL DEVICE

Requirements of IEC 62366 to main operations

The IEC 62366 requires to identify and document the main operations. For them, safety-critical features must be determined to be included in the verification and validation of serviceability.


Too bad that the norm forgets to define the term function. Maybe that is why some confusion in the informative annex occurs, with some examples. 

Which confusions they are, and which mistakes of your main operating functions of your medical device product you should avoid with the identification (and hence testing), you can view in a short (<5min) video.

IEC IEC 62366 calls in Appendix G.4.2 for examples of main operations like

  1. Turn on / off a device
  2. programming pump
  3. Infusion set insertion and replacement

But that is not correct: 1. is a function 2. is an object, and 3. are two subtasks. My "Usability Guru" Thomas Geis helped me with a definition:

Function (from a user perspective): "Control elements and Information on the user interface that are needed in carrying out a task with help of the system."

Examples of controls would be: "set flow", "zoom", "emergency stop" or  for example, in surgical tools, "cut", "lifting", "hold". Examples of information would be: "Current blood pressure", alarm "heart rate too low", feedback "lamp replacement required in 5 days"

Functions are implemented with "user interface elements" (such as a slider, push buttons, displays). For controls that are typically the "tools" of the user interface, information in the "usage objects" of the user interface.

When are functions to be classified as "common" and as "safety critical"?

When a function is "frequently" used or is classified as safety-critical, it was named one of IEC 62366 main operating functions.

Safety-critical functions

Whether an operating function is critical to safety, results from the risk analysis. If the patient, a user, or a third party may suffer a defect, it is critical to safety: In general for each function or each UI element as part of risk management, you can, and must, review what happens when the user

  1. Enters something wrong (or enters nothing) or
  2. Selects something wrong (or selects nothing) or
  3. Does not recognise something or recognises it wrongly.

In the recognition one distinguishes between the false reading (perception) and the wrong understanding (cognition).

Users can only enter, select and perform cognitive performances such as recognising, understanding and distinguishing. Precisely these requirements, to input, choose or recognise something on a system, which are the usage requirements .

Frequently used functions

You can deduce whether an operating function should be classified as frequently, if it is used as part of a core task. If so, the assumption that it is frequently used, should be true.

This requires, however, that you not only identify the usage requirements, but also the core task.

In the seminar " Usability, Requirements & IEC 62366", you will learn both. This seminar will provide you with all the knowledge and skills to

  • create an IEC 62366 compliant to the serviceability act,
  • identify the real needs of your users and thus develop (medical) products that deserve the title “innovative” and thus have the potential to "shake up " the market and
  • avoid unnecessary, time-consuming and cost-incurring iterations and consistent reworks of seemingly constantly changing requirements 

Checking the main operating functions

As stated above, it is important to check the following:

  1. That the specified requirements for the main operating functions are implemented
  2. That the user requirements are met (i.e. the user can enter, select and recognise something as planned ) and
  3. That (hence) users can obtain the best user objectives.

The test of 1. is equivalent to a usability verification, the 2nd and 3rd to the usability validation. Read more for the validation of medical devices (also the usability validation).

Functions, tasks and goals

The IEC 62366 uses the term "function" diligently, for example in the context of the main operating function, without having the concept of the term function defined at all. On the contrary, the way it is written above it confuses functions, tasks and objectives.

Thomas Geis helped me gather additional definitions:

  • Target: an intended working result (Source: ISO 9241-11)
  • Work task: The necessary measures for goal achievement activities (Source: ISO 9241-11). The activities required to achieve a desired working result (insertion of the first two terms)
  • Function: The user objects and tools that can be used from a user perspective to accomplish a work task.

The previous sentence is not an official definition of "function", one can deduce this definition from the Usability Guide of the DAkkS. It does not lack real definitions of the term function. Thomas Geis has found no less than 10 (!) definitions of the term function that I have summarised for you in the glossary.


Prof. Dr. Christian Johner

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