Tables, diagrams, text and other visuals can share what data show. Bar graphs compare things between groups. Line graphs track changes over time and are better than bar graphs when changes are small. Pie charts compare parts of a whole and do not show changes over time. An X-Y plot shows whether two things have a positive, negative or no relationship. On a bar graph the y-axis usually starts at 0 and is split into equal parts. A title tells what a graph shows, and a source line says where the data came from and gives credit to those who collected it.