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Embedded Systems December 2000 Vol13_13

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NIALL MURPHY , Principles of User Interface Design The placement of knobs, buttons, and switches is as essential to the making of a good product as the firmware. This article illustrates the delicate relationship between the two. here are lWO fundamental approaches to usabili ty. One is usability by evaluation; the other is usability by jJrinciples. Usabili ty by evaluation involves dissecting a design to find its strong and weak points with a view to making improvements. While this is a necessary part of the validation of any product, it is not the only way to invest in usabili- ty. Historically, a lot of usabili ty wo rk is done this way because usabil- ily is not considered until someone realizes that the product is hard to use. Nobody notices that it is hard to use until the product, or a sizable portion of i t, has been built. The easy part of usability by evaluation is criticizing the current design; the difficult part is deciding what would improve it. Usabili ty by principles is about deciding ahead of time what usabili ty proper- ties will be desirable on this interface, and what types of people will use it. By naming and defining these principl es, you will be equipped with a language that will allow the product's usabilily featu res to be discussed and documented more powerfully. I t also encourages transfer of usabili ly concepts from one product to another. Mo re importantly it allows you to decide what you want from the inter- face before you begin designing. Robustness We are used to thinking of robustness as a mechanical properly. It indicates how well the object tolerates rough use and carelessness. A robust user interface is not necessal-ily physically strong (though th at has otller obvious advantage ), but it tolerates improper inputs, or makes them impossible. A robust interface not only protects tile device from accidental damage due to an incorrect input, but also protects the user and tile entities tll at the device acts upon. Embedded Systems Programming DECEMBER 2000 55

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