You can’t design the user’s mental model directly. But you can design the
system image to convey the design model clearly (see figure 9.5). You should
also define your design model explicitly; to make sure it’s clear, consistent and
not overly technical or complex for your audience.
Figure 9.5: A system image: The Sunsprite Tracklight helps users monitor
their daylight exposure. The instructions explain what it does, how to interact
and data is displayed using the LEDs^5. (Image from^1
https://www.sunsprite.com/tracklight/).
Multi-device services are conceptually more complex
Back when Norman first wrote about conceptual models, a system was
generally a software application running on a standalone computer. Multi-
device services make conceptual models more complicated. There are not just
more interfaces, but more places where processing and functionality can live
and where data can be stored. Because there are more nodes and connections,
there are more points of failure and ways to fail. This is often where
complexity is exposed: when the system is working well, it may not matter
where your data or preferences are stored. But when parts or connections fail,
the user has to understand something about how the system works in order to
understand what is happening and why.