# How to: Create a Custom Summary Function

The following example demonstrates how to create a custom summary function, which returns an OHLC point calculated by the passed array of values. To accomplish this task, create a SummaryFunction delegate and register it using the ChartControl.RegisterSummaryFunction method:

``````// Declare the Financial summary function.
private static SeriesPoint[] CalculateProductValue(
Series series,
object argument,
string[] functionArguments,
DataSourceValues[] values,
object[] colors
) {
string functionArgument = functionArguments[0];
int lastIndex = values.Length - 1;

double open = Convert.ToDouble(values[0][functionArgument], CultureInfo.InvariantCulture);
double close = Convert.ToDouble(values[lastIndex][functionArgument], CultureInfo.InvariantCulture);
double high = Math.Max(open, close);
double low = Math.Min(open, close);
for (int i = 1; i < lastIndex; i++) {
high = Math.Max(high, Convert.ToDouble(values[i][functionArgument], CultureInfo.InvariantCulture));
low = Math.Min(low, Convert.ToDouble(values[i][functionArgument], CultureInfo.InvariantCulture));
}
// Return the result.
return new SeriesPoint[] {
new SeriesPoint(argument, high, low, open, close)
};
}

private void Form1_Load(object sender, EventArgs e) {
// Register the summary function in a chart.
chartControl.RegisterSummaryFunction(
name: "FINANCIAL",
displayName: "Financial",
resultScaleType: ScaleType.Numerical,
resultDimension: 4,
argumentDescriptions: new SummaryFunctionArgumentDescription[] {
new SummaryFunctionArgumentDescription("Value", ScaleType.Numerical)
},
function: CalculateProductValue
);

Series series = chartControl.Series["EurUsd"];
series.ArgumentDataMember = "DateTime";
// Note that ValueDataMembers are not specified.
series.DateTimeSummaryOptions.SummaryFunction = "FINANCIAL([Value])";
}
``````