What does Howard Wainer say in "Understanding Graphs and Tables" (1992) about how a graph or a table can provide three levels of information?

According to Howard Wainer in his 1992 essay "Understanding Graphs and Tables," a graph or a table can provide three levels of information:
1. "Elementary level questions involve data extraction, for example, 'What was petroleum use in 1980' " (Wainer, 16). This first level of information is the information you can learn from looking at a graph and simply finding the desired number, statistic, and so on. Factually, what is the data for this one point? This is the elementary level.
2. "Intermediate level questions involve trends seen in parts of the data, for example 'Between 1970 and 1985 how has the use of petroleum changed?' " (Wainer, 16). The intermediate level of information is good for identifying patterns in data. The first level was used to identify individual facts, but this second level can now start to put these individual data points together and allow the reader to recognize patterns.
3. "Overall level questions involve an understanding of the deep structure of the data being presented in their totality, usually comparing trends and seeing groupings, for example, 'Which fuel is predicted to show the most dramatic increase and use?' or 'Which fuels show the same pattern of growth?' " (Wainer, 16). This third level of information allows the reader to compare trends or patterns. Since the reader can compare the data, it allows him or her to make predictions or draw connections and inferences. This level allows the reader to get into really analyzing and using the data in a graph.