Graphical excellence consists of complex ideas communicated with clarity, precision and efficiency. The physical representation of numbers on the graph should be proportional to the numerical quantities represented. Clear, detailed and thorough labeling should be used to defeat graphical distortion and ambiguity. Show data variation, not design variation . Graphs should not quote the data out of context.
Scales are fundamental to conveying information in a graph.
Scales should be chosen so the data fill the data region and you have high resolution. Sometimes the appropriate scale can eliminate problems in detection due to overlapping data points. If you want to compare two graphs, the scales must be comparable. If zero is not important to the information in your data, then don't insist that it be included in your scale. When the important feature in the data is percent change or multiplicative factors, consider using a logarithmic scale.