Great post at the Duarte Blog (found here) about how people cheat with the charts to make information fit with their version of events.
By simply manipulating the length and height of axis units you can tell what look like very different stories. As Duarte describe it:
"The flexible grid: One of the easiest ways to give more or less movement to the trend of a curve is to expand or contract the horizontal or vertical axis of the chart. The chart below shows a correctly scaled trend and six ways the visual image changes by expanding or contracting the grid layout."