consistency of language, information graphics and aesthetics across online and
print materials. And you might also need to consider the continuity of any
processes that require users to refer between materials. Again, setup is a key
example: if your instruction booklet says ‘now the LED will blink for 2
seconds’, that’s a pointer to look at the other device. (Setup is covered in more
detail in chapter 10, Key interactions). Setting user expectations accurately is
also a form of continuity: if your marketing materials highlight a feature, it
should be easy to find the UI. If not, that’s a form of discontinuity.
The interusability model may not be complete for the broader service context,
but I have found it useful for thinking about interactions than span digital and
non-digital media.
Chapter summary
Conventional usability/UX is concerned with interactions between a user and a
single UI. Interusability deals with interactions across multiple devices. The
aim is to create a coherent UX across the whole system even when devices
have very different characteristics.
Users need to form a clear mental model of the overall system, although it can
be challenging for them to understand the interconnections between devices.
Designers need to distribute functionality between devices, to suit the
capabilities of each and context of use (composition).
They also need to determine which elements of the design should be consistent
across which parts of the system, for example terminology, platform
conventions, aesthetic styling and interaction architecture.
Data and content can sometimes be out of sync around the system, causing
continuity issues. Designers may need to find creative ways of dealing with
this in the UI. When interactions begin on one device and switch to another,
clear signposting is needed.