Behavioural design is probably more often referred to as usability, but the two terms essentially refer to the practical and functional aspects of a product or anything usable we are capable of using in our environment. Behavioural design is all about, how users carry out their activities, how quickly and accurately they can achieve their aims and objectives, how many errors the users make when carrying out certain tasks and how well the product accommodates both skilled and inexperienced users etc.. Behavioural design is perhaps the easiest to test, as performance levels can be measured once the physical (e.g., handles, buttons, grips, levers, switches, and keys) or usable parts of an object are changed or manipulated in some way. For instance, buttons responsible for two separate operations might be positioned at varying distances from one another so as to test how long it takes the user to carry out the two tasks consecutively. Alternatively, error rates might be measured using the same manipulations. Examples of experiences at the behavioural level include the pleasure derived from being able to find a contact and make a call immediately on a mobile phone, the ease of typing on a computer keyboard, the difficulty of typing on a small touchscreen device, such as an iPod Touch, and the enjoyment we feel when using a well-designed computer game controller etc. The behavioural level essentially refers to the emotions we feel as a result of either accomplishing or failing to complete our goals. When products/objects enable us to complete our goals with the minimum of difficulty and with little call for conscious effort, the emotions are likely to be positive ones. In contrast, when products restrict us, force us to translate or adjust our goals according to their limitations, or simply make us pay close attention when we are using them, we are more inclined to experience some negative emotion. Behavioural science is very important in user experience design. Designers should understand the psychology of each product users so that they design the product that users can admire and love.