Problem: How should the artifact indicate what kind of information should be supplied?
If high precision is needed (e.g. "73.6" on a scale of 1 to 100), two additional features become necessary: a display of the exact current value (usually text), and the ability to precisely adjust the value without superhumanly fine motor control. This is sometimes achieved by the workings of the control itself; for instance, large circular knobs (like a volume knob) allow for very fine control of a value, while also facilitating large value changes. Linear sliders aren't nearly as good at this. In the computer world, tiny value changes are sometimes made by clicking on buttons in or near the control, like the arrows at the tops and bottoms of scrollbars.
On the other hand, if precision is unnecessary, then there's no point in cluttering up a clean, simple implementation with extra displays and controls.
Resulting Context: Good Defaults may let the user look at the default value, judge it to be OK, and move on without even bothering to set the value. If you're not using a textual display of the current value, but the user might sometimes want to see it, Short Description could be used to show it on demand (as a form of Optional Detail On Demand). Pointer Shows Affordance can help indicate to the user that the control on the scale is manipulable.
This pattern works because it sets up a natural mapping between the
value and what the user sees. It's very powerful; you thus need to be careful
that the visual analogy is correct. Consider what would happen with a value
that changes logarithmically, for instance -- if you presented a linear
slider from 1 to 1,000,000, but numbers like 1, 10, and 100 are just as
likely to be picked as the numbers at the other end of the scale, those
small numbers will be impossible to pick out. In this case, you could transform
the problem to show a linear scale of the exponents of 10: 0, 1, 2, 3,
4, 5, 6. (In fact, Choice from a
Small Set might work even better.)
Copyright (c) 1999 by Jenifer Tidwell. All rights reserved.