UIs on different devices don’t all have to have the same features, but where
they do, the functionality should be consistent. For example, if a heating
controller supports a 6 phase schedule (6 phases throughout the day) but the
companion phone app only supports 4, users will wonder what happened to the
other two (see figure 9.26).
9.26 – Diagram: 6 versus 4 phase operation...
Consider the most likely combinations of devices
As a designer, you may have to think about design across a large ecosystem of
devices. Users may not have all of these. Focus your effort to achieve
consistency on the combinations of devices users are most likely to have. To
stick with the example of a heating system, all your users might have a
controller and smartphone app, but few will regularly use both iOS and
Android apps. So it’s important that the smartphone apps are both
appropriately consistent with the controller. It’s less important that knowledge
users acquire from using one smartphone app is transferable to the other. For
example, the location of the menu button, or the way that system settings are
grouped and accessed, need not be the same across mobile platforms but
should conform to the platform conventions (as discussed above under ‘Follow
platform conventions’). Few users will use both and those who do are likely to
be familiar with both conventions.
Continuity
What is continuity?
In the film industry, continuity editing ensures that different shots flow in a
coherent sequence, even if they were filmed in a different order. It would be
disrupting to the narrative if a character’s hairstyle changed within a scene,
furniture moved around, or a broken window was suddenly intact again^15.
In cross-platform interaction design, continuity refers to the flow of data and
interactions in a coherent sequence across devices. The user should feel as if
(^15) Spotting continuity errors in movies is a sport. Sharp-eyed viewers share the errors
they have spotted on websites such as http://www.moviemistakes.com,.