Chapter 6: User Interfaces for Mobile Media 243 6.4.1 Common UI Design Guidelines Before introducing the design process, we review a few important principles that should affect the UI design. A myriad of “UI design principles” exists; perhaps the most famous ones are those by Nielsen (1994) and Shneiderman (1998). These principles form the corner- stone of a good UI in general, but they are even more important in mobile devices, as the users have no opportunity to read a manual when they are on the move. Next, we summarize our UI rules. 6.4.1.1 Keep It Simple! Among all the important design principles, simplicity is the one above all others. Use common sense and try and avoid any complex and “exotic” design solutions. To exaggerate a little, the world is full of wonderful inventions that are too diffi cult to use, for everyone except the designer. Fancy designs often demand a lot of labour during dif- ferent phases in the product lifecycle: when being designed, imple- mented, tested, and – fi nally – when the users start to learn to use the system. There is, in most cases, no comparison to the gained benefi t. Instead, the best way to create usable user interfaces is to compare different solutions – traditional and radical, improve, innovate, test and iterate the design, listen to the users’ voice, and – use loads of common sense. A simple design should make it predictable what can be done now or what to do next, as the actions form a logical sequence with clear start and end points. When things are visible in the user interface, the user’s cognitive and short-term memory load are reduced. The user should not have to remember what was on the previous screen; instead the system should provide the necessary information and cues. Also, the design should contain aspects that are familiar to the user as well as being easy and quick to learn. 6.4.1.2 User Controls Everything! Users – especially those with a lot of experience – wish to feel in control. Therefore, the system should provide timely feedback on the user’s actions, so that they know what they are related to. For frequent actions, feedback should not disturb the task fl ow. A rule of thumb is that feedback is considered instant if the system has provided a response within 0.1 seconds. One second is considered to be the limit for the user’s fl ow of thoughts to remain undisturbed, even though the user will notice a delay of such a length. Beyond this, the system should provide some indication about the delay and ten seconds is the maximum to keep