Chapter 6: User Interfaces for Mobile Media 221 acters # and * (ITU). To input text, three or four characters are assigned to each number key. For example, to type the letter “B” the user presses the key “2” twice, since letters A, B, and C are assigned to this key. Other text entry methods include those based on predicting the 8 word that the user is typing, such as T9. Also, other keypad layouts, QWERTY among others, exist. If a device is not equipped with a full QWERTY keyboard, the mode of the character entry should be displayed. For example, does a key press in an ITU-T keyboard generate a number, a character, or a symbol? To facilitate eyes-free use of the keys, they often have markers or distinctive shapes. For example, in ITU-T alpha, the 5 key has a physical “bump” that is recognized by the fi nger. In addition to the numeric keypad, Figure 6-5 also shows an example of dedicated media keys on the cover of the slide that are used for controlling music playback. Most mobile devices must have an input device for moving a selec- tion or pointing to an object on a screen. For discrete input, they 9 usually employ a 2- or 4-way joystick, a rocker key, or cursor keys. Half-cardinal points, such as north-east, are not typically supported since they could produce unintentional navigation steps when the device is operated while moving. A 4-way input device may contain a so-called centre select. Once the centre of the device is pressed down, the device effectively trans- fers into a 5-way joystick (Figure 6-5). If they do not contain such a device, a soft key or a dedicated hardware key is used for selection. Another solution for changing the selection, in a way that the user can adjust the speed, is by using a scroll wheel; the selection can be confi rmed by pressing the wheel in. The wheel is used by forefi nger or thumb, depending on its placement that varies from the front (as in Apple iPod) or to the side (as in RIM Blackberry or SonyEricsson P990i). In Apple iPod, on the contrary, Click Wheel is a dual purpose input device. If the user rotates a thumb on it, the wheel can be used for scrolling, but if the user taps cardinal points near the wheel’s edge, those locations act as buttons (iPod; RIM; P990i). For continuous input, some mobile devices are equipped with a touch-sensitive screen to move a cursor and select objects with a stylus (a pen) or a fi nger. To input text, the user can draw the characters directly on the screen. In handwriting recognition, the system interprets the pen gestures as characters and sends them to the application as 8 http://www.t9.com/ 9 Rocker key combines several cursor keys to a single key that can be tilted (rocked) to left, right, down, or up when pressed in that direction.