You are a web developer at your advertising company. One of
the tasks assigned is to display some ads on the main web page that is going to
change every 3 seconds. The page size is big, and the only thing that is
required to change. Therefore, there is no need to change any other parts of
the page. Another example would be changing stocks prices every 2 seconds or
even if you are processing a number of records to show the remaining to be
processed.