The chart tag apparently auto-sizes the Y-axis based on maximum y-value in the chart. This behavior is not appropriate when creating multiple charts for users to compare.

A "y-maximum" or "y-range" attribute is required to specify the maximum y-value of a chart, on a per-chart basis. The presence of this attribute should disable JFreeChart's "AutoRange" behavior, and call ValueAxis.setUpperBound to the specified value.

Additionally, if the "y-format" is PERCENT, the "y-maximum" attribute should accept a a percentage value. Not required, just a a nice-to-have enhancement.