The nature of user interaction plays a far more important role in the design of applications for small-screen devices than in the design of applications for desktop computers. This is partly because there are fewer standardised forms of input or, more simply, no clear equivalent to the keyboard and the mouse. In addition, the context for small-screen device use is far less predictable than for a conventional desktop computer. Even the comparatively mobile use of a laptop computer requires the user to be in a static, seated position. For those portable devices that are often more peripheral in their use, the design options for the menu structures and screen layout will depend far more on the user's likely interaction style. Physical interaction Interaction with small-screen devices reveals the conflict of interests between creating the smallest physical size that will give the user unrestricted mobility and flexibility, whilst maintaining dimensions that are defined by the size and the motor functions of the human hand. The balance is not always achieved and some devices are already smaller than the minimum size that can be comfor tably operated by an adult hand. There are two fundamental types of physical interaction that can be distinguished: one-handed and two-handed interaction. Some devices can only be operated with two hands, for example, the Game Boy, whilst other