Graphics are instruments for reasoning about quantitative information. Often the most effective way to describe, explain, and summarize a set of numbers is to look at a picture of the numbers. Well-designed data graphics are the simplest and most powerful method of analyzing and communicating numerical information. It is simple to make and read, and most useful for plotting continious data to show trends and relationships. Although a bar chart may better show dramatic comparisons of amount, the ability to use several curves on the same line graph makes the line graph superior.
Bar charts represent values or amounts by bars of scaled lengths.
Bars may be arranged vertically of horizontally, depending on the number and type of variables to be displayed. Bars should be the same width with equal spacing between them, yet close enough together to make comparison easy. If it is necessary to provide the exact value represented by each bar, the values should be placed someplace other than at the ends of the bars since this may increase their apparent length. The title should describe the variables and their relationship, the source of the information and the observer, and the date. Place the title at the top of the sheet.