We have an old RadChart control and a new ChartView
set of controls. The new control is much faster than the old component, it resolves many limitations the RadChart has, it is very flexible and easy to set up. If you are indeed using the old RadChart and you have not yet integrated it in your application, we strongly suggest you remove it completely and use the chartview. The answer below concerns a RadCartesianChart (one of the ChartView controls) and not RadChart.
Even though the chart calculates the values in percentages, the individual series does not know about the rest of the series and there is no direct way you can get the percentage.
You can create a new Percent property in your actual business item and calculate the percent in your models. Later you can use the LabelDefinition property of the series and specify a Binding (look for the Binding property of the ChartSeiesLabelDefinition), Binding="Percent". Let us know how it goes.
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