Consider the following data on the thickness of sockets produced by a process.
Apart from seeing that the numbers are different, it is not too easy to detect anything meaningful from this data. All you can really say on first analysis is that the size of the sockets produced seems to vary over time.
Data presented in this way is very difficult for a human being to process and interpret quickly. Unfortunately, we often have to make decisions based on large amounts of data, and these decisions may need to be made quickly. As the following section shows, presenting the data in a suitable graphical format, instead of as a table of figures can significantly improve our ability to process the information.