Small changes over time, not starting the y-axis at zero
Time series charts do not have to begin at zero, if a chart does not start at zero this must be indicated by breaking the y-axis in an obvious way.
A chart can tell a very different story depending on the scale of the axes.
This chart gives the impression that the measles, mumps and rubella (MMR) vaccination level has remained high and fairly stable.
An overview
MMR vaccination uptake at age 1 year
UK, 1992 to 2012
When the y-axis is altered a different picture emerges showing that the measles, mumps and rubella vaccination has dropped considerably since 1997.
A more focused view
MMR and Diphtheria vaccination uptake at age 1 year
UK, 1992 to 2012
You can use two charts with different axes scales to ensure that the data are represented without bias whilst highlighting the important message.