1 Begin the vertical axis at zero. Doing so ensures that the depicted magnitude of change in the data accurately reflects the actual change in the data. To see the importance of this rule, compare Figure 14-9, which follows this principle, to Figure 14-10 ( see next page), which does not. Exception: Beginning the vertical axis at a value other than zero may be useful if there is a need to monitor minor fluctuations in the data (see Figure 14-11 on the next page).