Problem: How can the artifact best present the actions that the user may take?
When someone uses the controls, give immediate feedback that something
is happening; this could be visual feedback, verbal, aural, tactile, etc.
The best controls are often those that also display the current state (thus
combining Control Panel with Status Display),
since it makes sense to people to affect something in the same place they
If the thing(s) being controlled has an obvious and familiar spatial layout, use it in the control panel. In The Design of Everyday Things, Don Norman makes an example out of stoves -- their burners are arranged in a 2x2 grid, but the controls for them are usually not, and users have to stop and think about which goes with which. If analogous spatial arrangement doesn't make sense in a given situation, then try instead to group the controls semantically. Ideally, the controls relevant to a given high-level task will end up clustered together (Small Groups of Related Things), so the user doesn't have to hunt all over the control panel for the next needed control.
Resulting Context: Appropriate controls now have to be chosen. Some patterns you can use are Choice from a Small Set, Choice from a Large Set, Sliding Scale, or even an interactive Chart or Graph. Make it clear which controls represent artifact-wide actions (see Convenient Environment Actions), and which represent actions upon one object (see Localized Object Actions) -- and indicate which object is being acted upon, of course!. When a given control is not meant to be used at a given time, disable it (Disabled Irrelevant Things).
To help naive users figure out what's what on a counterintuitive display, or on one that's meant for experts, you could employ Short Description or Optional Detail On Demand. To alert the user to side effects and to unexpected situations, use Reality Check and Important Message, respectively.
Copyright (c) 1999 by Jenifer Tidwell. All rights reserved.