Specifications

35
Touch User Interface
The application program is the interface
between the user and the computer system.
The application program presents displays,
accepts user input, and takes action based on
that input. The design and organization of
the program is critical to the successful use
of the touch system, especially when the end
users are likely to be novices.
Interface Design Factors
To maintain the natural simplicity of the
touch interface and to lead the user easily
through the program, the interface designer
should be aware of several different factors.
n Target Location
Touch target location on the screen is
determined by the relative importance of the
target. Consistency must also be considered.
The user will locate targets with greater
speed, less confusion, and fewer errors when
targets of the same or similar function are
consistently located in the same relative
location on the screen.
n Number Of Targets
The number of targets per screen should
be limited to as few as possible, balanced by
the difficulty of switching screens. Nesting
and prioritizing relieve the need to crowd
targets on the screen, hence reducing the
potential for human error. In the case of
menus, more items can be put on the screen.
But, if menus are nested too deeply, users
will soon tire of searching through the
menus. The use of graphic symbols (icons)
for touch targets can be effective in helping
the user identify targets quickly.
n Target Size
The size of targets is limited by the
stylus size. Error rates can be lowered by
increasing the size of the targets. When
designing targets for finger activation,
research has shown that few fingertips are
more than 22 millimeters across. Each target
should be surrounded with a guard band or
dead zone, where touches are not
recognized. Guard bands reduce the
possibility of user confusion and frustration
by eliminating the possibility of activating
an adjacent target.