"We think of the term "usability" as applying to the user's experience with a device and its many capabilities. But usability is more than a measure of rich functionality or a beautiful UI; no matter how sophisticated or attractive, if something doesn't work well out of the box, it will not rate as highly usable. Most consumer electronics and appliance manufacturers have learned this lesson the hard way and now design their products with this in mind.
Cars, TVs, digital cameras, music players, even household appliances are designed so that they work out of the box, with minimal effort and without requiring elaborate setup. For example, the most you might need to do to set up your new digital camera when you take it out of the box is set the clock. Beyond that, the most popular digital cameras are designed so that everything works with minimal effort. In a contrasting example, most smartphones have rich and attractive UIs, but configuring the email to work on any of them is an entirely different proposition. The device itself may appear to be highly usable, but if the email application on it is complex to set up and use, that will affect the perception of the overall usability of that device.
One good metric that can help us determine the usability of a new device or service is the "twiddling factor" - the number of settings that need to be manually set and reset to use a particular service or capability. In a world where everything is connected, services can become increasingly complex. Not only does the device need to work properly for the service to work, but a number of interconnected entities - from the application on the device to the network and any remote services used by the application - need to work together as well.
Consider the lawn sprinkler. A stand alone lawn sprinkler works when the water is turned on. Imagine that same sprinkler capable of internet connectivity for checking on local weather conditions and adjusting water levels and timing accordingly. The best possible user experience with that sprinkler will occur if the effort to run it is the same as in the case of the stand alone sprinkler. But it is a complex task to provide this level of usability; network connectivity, security settings, and remote services would all need to work in harmony and mask failures in order to provide the same level of usability as a stand alone sprinkler. Clearly a significant amount of behind-the-scenes functionality would be needed to reduce the twiddling factor of a "smart" lawn sprinkler to the same level as that of a stand alone sprinkler.
With mobile devices, the number of the entities involved in delivering new services and the complexity of the associations among these entities is increasing rapidly. So one good metric for determining the usability of a new service is how much twiddling is required during the lifecycle of that service. The aim of any mobile device or service management system should be to reduce this twiddling factor to a bare minimum-as close to zero as possible.
Overall usability involves many factors. However, the richest customer experience for any service (and the highest degree of usability) comes when that service can be used with little or no twiddling. Services that require a great deal of twiddling, either during setup or use, can never really be considered highly usable, regardless of their other attributes. To achieve a high degree of usability for new services in an interconnected world, the entire ecosystem needs to be designed for manageability-from the devices and services themselves, to the management systems supporting them. Support for usability capabilities such as plug-and-play, discovery, auto-configure, auto-repair and the like cannot just be features of individual devices but instead must become features of the entire mobile ecosystem." (Continued via telecoms.com, ) [Usability Resources]