Trackball and thumbwheel

Trackball and thumbwheel
The trackball is really just an upside-down mouse! A weighted ball faces upwards and
is rotated inside a static housing, the motion being detected in the same way as for
a mechanical mouse, and the relative motion of the ball moves the cursor. Because
of this, the trackball requires no additional space in which to operate, and is therefore a very compact device. It is an indirect device, and requires separate buttons
for selection. It is fairly accurate, but is hard to draw with, as long movements are
difficult. Trackballs now appear in a wide variety of sizes, the most usual being about
the same as a golf ball, with a number of larger and smaller devices available. The size
and ‘feel’ of the trackball itself affords significant differences in the usability of the
device: its weight, rolling resistance and texture all contribute to the overall effect.
Some of the smaller devices have been used in notebook and portable computers,
but more commonly trackpads or nipples are used. They are often sold as alternatives to mice on desktop computers, especially for RSI sufferers. They are also
heavily used in video games where their highly responsive behavior, including being
able to spin the ball, is ideally suited to the demands of play.
Thumbwheels are different in that they have two orthogonal dials to control the
cursor position. Such a device is very cheap, but slow, and it is difficult to manipulate the cursor in any way other than horizontally or vertically. This limitation can
sometimes be a useful constraint in the right application. For instance, in CAD the
designer is almost always concerned with exact verticals and horizontals, and a
device that provides such constraints is very useful, which accounts for the appearance of thumbwheels in CAD systems. Another successful application for such a
device has been in a drawing game such as Etch-a-Sketch in which straight lines can
be created on a simple screen, since the predominance of straight lines in simple
drawings means that the motion restrictions are an advantage rather than a handicap. However, if you were to try to write your signature using a thumbwheel, the
limitations would be all too apparent. The appropriateness of the device depends on
the task to be performed.
Although two-axis thumbwheels are not heavily used in mainstream applications,
single thumbwheels are often included on a standard mouse in order to offer an
alternative means to scroll documents. Normally scrolling requires you to grab the
scroll bar with the mouse cursor and drag it down. For large documents it is hard to
2.3 Positioning, pointing and drawing 75
be accurate and in addition the mouse dragging is done holding a finger down which
adds to hand strain. In contrast the small scroll wheel allows comparatively intuitive
and fast scrolling, simply rotating the wheel to move the page.