Bar graphs are excellent ways to show results that are one time,that aren't continuous - especially samplings such as surveys, inventories, etc A bar chart is marked off with a series of lines called grid lines. These lines typically mark off a numerical point in the series of numbers on the axis or line. In this case, each grid line going up and down marks a multiple of 20 as the graph is divided. More grid lines can make it easier to be exact with the amounts being shown on the bar graph, but too many can make it confusing. Notice that for data that does not fall evenly on a multiple of 20, the bar is in between two grid lines. Bar graphs are useful to get an overall idea of trends in responses.