7?2 Principle
Since human brain has some limits on its capacity for processing information, it deals with complexity dividing information into chunks and units. According to George A. Miller?s studies humans? short term memory can retain only about 5-9 things at one time. This fact is often used as an argument for limiting the number of options in navigation menus to 7; however there are heated debates about The Myth of ?Seven, Plus or Minus 2?. Therefore it?s not clear how the 7?2 Principle can, could or should be applied to the Web. Miller?s studies.

2-Second-Rule
A loose principle that a user shouldn?t need to wait more than 2 seconds for certain types of system response, such as application-switching and application launch time. The choice of 2 seconds is somewhat arbitrary, but a reasonable order of magnitude. Reliable principle: the less users have to wait, the better is the user experience. [UF]

3-Click-Rule
According to this rule users stop using the site if they aren?t able to find the information or access the site feature within 3 mouse clicks. In other words, the rule emphasizes the importance of clear navigation, logical structure and easy-to-follow site hierarchy. In most situations the number of clicks is irrelevant; what is really important is that visitors always know where they are, where they were and where they can go next. Even 10 clicks are OK if users feel that they have a full understanding of how the system works.

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