The sizes and capabilities of the human frame and senses have been well cataloged these studies form the science of ergonomics. Design a human-machine interface in accord with the abilities and foibles of humankind, and you will help the user to not only get the job done but also be a happier, more productive person.ĭesign guidelines for products that interact with us physically are reasonably straightforward. Use a machine or a tool in accord with its strengths and limitations, and it will do a good job for you. Inscription at the Delphic Oracle, from Plutarch, Morals Ergonomics and Cognetics: What We Can and Cannot Do To the extend that doing so does not conflict with these essentials, an interface should also be attractive.2-1. An interface should be effective, habituating, reliable, efficient, and tested. All of the principles, if followed, create learnable interfaces. When use of the interface has become habitual, these elements go unnoticed. But these are of secondary importance in terms of task completion. How messages are phrased is important, how the interface looks is also important. The fifth principle: An interface should be pleasant in tone and visually attractive.Ĭommentary. It is never the user's fault, but also remember that people find it difficult to change, so difficulties based on previous habits may not be dispositive. One must test, objectively observe, and modify the interface if testing shows that users have difficulties. All of the theory in the world, and the wisest guru, cannot always predict how an interface will work in practice. The fourth principle: The suitability of an interface can only be determined by testing.Ĭommentary. Another set of techniques and measures can be used to help judge learnability. The GOMS model and information theoretic measures of efficiency (to name two particular techniques among many) must be mastered and used by interface designers. Quantitative measures should be used, and an interface should be close to its theoretical minimum in terms of the time it takes to do an operation.Ĭommentary.
Good engineering practices should be applied to interface design. An interface should not take more of your time than is necessary, either in use or in learning. The third princple: An interface should be efficient and as simple as possible.Ĭommentary. Rule 2: The system should neither lose your work nor through inaction allow your work to be lost. This is often not thought of as a property of an interface, but one can build a reliable interface on top of an unreliable system (of the order of unreliability of todays operating systems).
Aside from not crashing, the system should never lose any work you have done or any information you have received or retrieved, even if you make a mistake or are forgetful. The second principle: An interface should be reliable.Ĭommentary. Crudely, there should be only one way to achieve a single-gesture subtask. "Monotony" here is a technical term meaning that you do not have to choose among multiple gestures to achieve a particular sub-task. To make an interface habituating, it must be monotonous.Ĭommentary. In the presence of modes, you will sometimes make mode errors, where you make a gesture intending to have one result but get a different and unexpected result, distracting you from your task. Modes exist where the same gesture yields different results depending on system state at a time when your attention is not on system state. To make an interface habituating, it must be modeless.Ĭommentary. Any interface will have elements that are habituating, but the principle here is to make the entire interface habituating. If the interface can be operated habitually then, after you have used it for a while, its use becomes automatic and you can release all your attention to the task you are trying to achieve. An interface should be habituating.Ĭommentary. That is not all that is needed, but it is a prerequisite. A understanding of the relevant portions of cognitive psychology, ergonomics, and cognetics is essential. Designing a human-machine interface demands that both the human and the machine be understood as well as possible. For a more experienced typist, typing the word "the" is a gesture.Ĭommentary. Example: For a beginning typist, typing the letter "t" is a gesture. When using a product to help you do a task, the product should only help and never distract you from the task.ĭefinition: A gesture is an action that you finish without conscious thought once you have started it. A nearly one page summary of design rulesĮ-mail from Jef Raskin to Tom Gilb, with kind permission by Tom Gilb The first principle.
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