Enhance Medical Device Usability: Just CRAP It

Usability engineering is rapidly gaining focus in medical devices. The very fact that IEC 62366 is applicable to all medical devices is proof of this. Products undergoing CE certification are expected to demonstrate compliance with usability engineering standards.

Jayaraman Kiruthi Vasan

In his e-book, Bright Ideas for User Experience Designers, David Travis stresses the need to apply various UX ideas. He mentions four principles that could do wonders in boosting any product's usability factor. He borrows the acronym CRAP, which was originally given to the process by another designer, Robin Williams (no, not Mrs. Doubtfire).

CRAP stands for contrast, repetition, alignment, and proximity. I think it would be appropriate to apply these four principles to a medical device design. Let's see what each of these principles means in the medical device context.

Capturing user attention is the primary goal of any user interface. Decision making can be made easier if controls/buttons are easy to distinguish from one another. Contrast can mean differences in size, fonts, colour, and/or form factor. A big red emergency button on a cardiac treadmill and the discharge button on defibrillator paddles are designed for immediate visibility. We could also see a big button marked "Alarm Mute" on a patient monitor. In the electrosurgical unit (ESU) shown above, the mode button is bigger than the other buttons.


Repetition in this case means consistency in presentation. Presenting similar information in similar ways helps enhance usability. For example, using the same kind of symbols to represent similar action keys could improve consistency and help users readily understand the functionality. Keys for increasing and decreasing values could use same up and down arrow symbols in all the screens and front panels.

A uniform alignment pattern in positioning the controls and displays can train the user to look for similar patterns. This makes navigation easier and faster. Let us consider an ESU. The up and down keys for setting output power in watts could be positioned in alignment with their related power display. The users relate these keys to the display and expect/assume/decide that they could expect a response from the display by using these keys.

Grouping together controls/buttons that initiate similar or related actions helps users relate to the relevant functions. In menu structures, hierarchical grouping could prove valuable in making user interface seamless. The power setting keys of the ESU we mentioned could be grouped with their related displays. For other modes, the grouping could be repeated to develop an easily understandable pattern.

CRAP is not just about cosmetic changes. It involves positioning, hierarchical grouping, consistent presentation, and unambiguous representation of features and actions.

Do you think this method could be applied to all medical devices? Do you know a device that may not be suited for these principles?

Stay relevant as a medical device packaging engineer

Jayaraman Kiruthi Vasan, Consultant - Electromechanical Systems, Healthcare Technology Innovation Centre, Indian Institute Of Technology, Madras

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