Some series types let you specify a minimum value for the elements drawn on the screen. For example, in a ColumnChart control, you can specify the base value of the column. To specify a base value (or minimum) for the column, set the value of the series object's minField property to the data provider field.

You can specify the minField property for the following chart series types:

• AreaSeries
• BarSeries
• ColumnSeries

Setting a value for the minField property creates two values on the axis for each data point in an area; for example:

<?xml version="1.0"?>
<!-- charts/MinField.mxml -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">
  <mx:Script><![CDATA[
     import mx.collections.ArrayCollection;
     [Bindable]
     public var expenses:ArrayCollection = new ArrayCollection([
        {Month:"Jan", Profit:2000, Expenses:1500, Amount:450},
        {Month:"Feb", Profit:1000, Expenses:200, Amount:600},
        {Month:"Mar", Profit:1500, Expenses:500, Amount:300}
     ]);
  ]]></mx:Script>
  <mx:Panel title="Area Chart">
     <mx:AreaChart id="myChart"
        dataProvider="{expenses}" 
        showDataTips="true"
     >
        <mx:horizontalAxis>
           <mx:CategoryAxis 
                dataProvider="{expenses}" 
                categoryField="Month"
           />
        </mx:horizontalAxis>
        <mx:series>
           <mx:AreaSeries 
                yField="Profit" 
                minField="Expenses"
                displayName="Profit"
            />
        </mx:series>
     </mx:AreaChart>
     <mx:Legend dataProvider="{myChart}"/>
  </mx:Panel>
</mx:Application>
The executing SWF file for the previous example is shown below:

The resulting DataTip labels the current value "high" and the minField value "low." The following example shows an AreaChart that defines the base of each column:

For an example of using the minField property to create a waterfall or cascading ColumnChart control, see Using column charts.

You can also use the baseAtZero property to determine whether or not the axis starts at zero. Set this property to true to start the axis at zero; set it to false to let Flex determine a reasonable starting value relative to the values along the axis.