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Understanding Graphs
Graphs are pictures of information, not pictures of things. The information in graphs is often called data. The most common kinds of graphs are line graphs, pie graphs, and bar graphs.

Line Graph
A line graph shows how things change over time. It starts with an L-shaped grid. The horizontal line of the grid stands for passing time (seconds, minutes, years, or even centuries). The vertical line of the grid shows the subject of the graph. The subject of this graph is the change in global surface temperature.