Chart limits are the minimum & maximum y-axis values. FusionCharts automatically calculates the best chart limits when you don't specify them explicitly.
The XML code going into the above is:
<chart caption='Monthly Revenue' xAxisName='Month' yAxisName='Revenue' numberPrefix='$' showValues='0'>
<set label='Jan' value='420000' />
<set label='Feb' value='910000' />
<set label='Mar' value='720000' />
<set label='Apr' value='550000' />
....
</chart>
Note that the chart limits have not been defined.
You can set the chart limits explicitly using the yAxisMaxValue and yAxisMinValue attributes.
<chart yAxisMinValue='0' yAxisMaxValue='100' ...>
However, in this case, when you are using the column chart, the zero plane would come up in a non-equidistant position.
You can set whether the y-axis lower limit would be 0 (in case of all positive values on chart) or should the y-axis lower limit adapt itself to a different figure based on values provided to the chart.
<chart caption='Monthly Revenue' xAxisName='Month' yAxisName='Revenue' numberPrefix='$' showValues='0' setAdaptiveYMin='1' >
<set label='Jan' value='420000' />
<set label='Feb' value='910000' />
<set label='Mar' value='720000' />
<set label='Apr' value='550000' />
....
</chart>
Note the change in the y-axis minimum value now: