A Menu with 200 Items

Smart products like mobile phones are increasingly made out of software. They are powered by general-purpose processors and supplied with several megabytes of memory. The displays are small, but resolution is improving and many manufacturers have introduced color screens. This sort of platform presents an opportunity to create a vast number of features without incurring any extra costs in hardware. The costs of software design and implementation are minor when divided by the number of similar products produced. This implies that whenever there is extra memory, developers will fill it with features. It would seem a waste of memory and processing power not to.

Market-driven pressures to increase the number of features in mobile phones are continual. By increasing their functionality, the products can be made to appeal to a larger market segment. The more features there are, the more likely it is that consumers will find some that they feel they need (see, e.g., the results by Pekkarinen and Salo in Chapter 10). Sometimes consumers can’t try out a real product when purchasing a mobile phone. Perhaps they have access to a dummy model, or (more likely) can only view the models locked in a glass display case. In those cases, the length of the feature list is a strong sales argument.

How do those features manifest themselves to the user? In a mobile phone, all features are accessed with a small number of keys, some of which can be activated in different modes. Such keys change their behavior according to current phone status at the moment they are pressed. Typically, the features of a mobile phone are organized as a hierarchical menu structure (see Figure 12.1 and Chapter 2).

Figure 12.1: 3310 phone menu hierarchy illustration.

Let’s make a highly simplified calculation of the average mobile phone feature set. The hierarchical menu structure of a mobile phone is like a tree; each function can be accessed from the root of the tree (main menu) through several branches (submenus) down to the desired function (leaf). The tree is called balanced if all the leaves are equally as many branches away from the root. If all the approximately 200 features of the Nokia 3310 phone were arranged in the menu as a balanced tree, we could minimize the average number of key presses that a user is required to make. Selecting the menu requires one key press (menu softkey), moving to the next menu item one key press (arrow down), and selection of either another submenu or a feature one key press (select softkey). With a balanced tree, the average number of key presses exceeds 12. A phone that requires users to make a dozen selections in order to complete a frequently undertaken task, like placing a call, is not a usable device.

A mobile product must be small to be carried and held in one hand with ease. There is simply not enough room for many more keys. Nor can key size be reduced much more because of the limits of human physiology. On the other hand, research by Keinonen^[1] shows that the user’s perception of a product’s usability depends on the number of keys on the product; more keys equal a product that is harder to use. If consumers want a phone that is particularly easy to use, they will probably select the one that has the fewest buttons. This behavior can lead to disappointment—what looks easy to use may actually be complicated to operate because of the vast number of features it contains.

Some researchers have explored ways of minimizing the number of keys on a mobile phone. Harri Wikberg describes a user interface with just one key,^[2] and some Asian manufacturers have sold single-key numeric pagers. Although these efforts are largely regarded as curiosities, it is still important to push the limits of how minimal user interfaces can be and yet retain a degree of ease of use.

Interaction designers of mobile phones face a challenging, almost paradoxical task. The number of features is rapidly increasing. At the same time, the number of user interface (UI) controls with which to access features is being reduced.

^[1]Many users fool the automatic alphabetic order by adding a prefix to the important people, for example, writing “AAA—Johanna” instead of “Johanna.”

^[2]T. Keinonen, One-Dimensional Usability—Influence of Usability on Consumer’s Product Preference, PhD dissertation, University of Industrial Arts, Helsinki, 1998.