Sub SetCellAggregationType( _
   ByVal row As Integer, _
   ByVal col As Integer, _
   ByVal type As AggregationType _
) 

Dim instance As IAggregationSupport
Dim row As Integer
Dim col As Integer
Dim type As AggregationType
 
instance.SetCellAggregationType(row, col, type)

void SetCellAggregationType( 
   int row,
   int col,
   AggregationType type
)

private void Form1_Load(object sender, EventArgs e)
 {
  fpSpread1.Sheets[0].RowCount = 8;
  fpSpread1.Sheets[0].ColumnCount = 15;
  fpSpread1.Sheets[0].GroupBarInfo.Visible = true;
  fpSpread1.Sheets[0].AllowGroup = true;
  fpSpread1.Sheets[0].GroupFooterVisible = true;
  fpSpread1.Sheets[0].ColumnFooter.Visible = true;
  fpSpread1.Sheets[0].ColumnFooter.RowCount = 2;
  fpSpread1.Sheets[0].ColumnFooter.Columns[12].HorizontalAlignment = FarPoint.Win.Spread.CellHorizontalAlignment.Left;
  fpSpread1.Sheets[0].ColumnFooter.Cells[0, 12].RowSpan = 2;
  //Value

     for (int r = 0; r < fpSpread1.Sheets[0].RowCount; r++)
       {
          for (int j = 0; j < fpSpread1.Sheets[0].ColumnCount; j++)
          {
           fpSpread1.Sheets[0].Models.Data.SetValue(r, j, j + r * fpSpread1.Sheets[0].ColumnCount);
          }
       }

       int i = 0;
       fpSpread1.Sheets[0].ColumnFooter.SetAggregationType(0, 1, FarPoint.Win.Spread.Model.AggregationType.Sum);
       fpSpread1.Sheets[0].ColumnFooter.Cells[0, i].Value = "Sum";
 }

private void fpSpread1_Grouped(object sender, EventArgs e)
 {
  FarPoint.Win.Spread.Model.GroupDataModel gdm;
  gdm = (FarPoint.Win.Spread.Model.GroupDataModel)fpSpread1.ActiveSheet.Models.Data;
  gdm.GroupFooterVisible = true;
  FarPoint.Win.Spread.Model.Group g1 = (FarPoint.Win.Spread.Model.Group)gdm.Groups[1];           
  ((FarPoint.Win.Spread.Model.IAggregationSupport)g1.GroupFooter.DataModel).SetCellAggregationType(0, 0, FarPoint.Win.Spread.Model.AggregationType.Sum);
  fpSpread1.ActiveSheet.Models.Data = gdm;
  }

  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
      FpSpread1.Sheets(0).RowCount = 8
      FpSpread1.Sheets(0).ColumnCount = 15
      FpSpread1.Sheets(0).GroupBarInfo.Visible = True
      FpSpread1.Sheets(0).AllowGroup = True
      FpSpread1.Sheets(0).GroupFooterVisible = True
      FpSpread1.Sheets(0).ColumnFooter.Visible = True
      FpSpread1.Sheets(0).ColumnFooter.RowCount = 2
FpSpread1.Sheets(0).ColumnFooter.Columns(12).HorizontalAlignment = FarPoint.Win.Spread.CellHorizontalAlignment.Left
      'Value
      Dim r As Integer
      Dim j As Integer
      For r = 0 To FpSpread1.Sheets(0).RowCount
          For j = 0 To FpSpread1.Sheets(0).ColumnCount
              FpSpread1.Sheets(0).Models.Data.SetValue(r, j, j + r * FpSpread1.Sheets(0).ColumnCount)
          Next j
      Next r
      Dim i As Integer
      i = 0
      FpSpread1.Sheets(0).ColumnFooter.SetAggregationType(0, 1, FarPoint.Win.Spread.Model.AggregationType.Sum)
      FpSpread1.Sheets(0).ColumnFooter.Cells(0, i).Value = "Sum"
  End Sub

  Private Sub FpSpread1_Grouped(ByVal sender As Object, ByVal e As System.EventArgs) Handles FpSpread1.Grouped
      Dim gdm As FarPoint.Win.Spread.Model.GroupDataModel
      Dim g1 As FarPoint.Win.Spread.Model.Group
      gdm = FpSpread1.Sheets(0).Models.Data
      gdm.GroupFooterVisible = True
      g1 = gdm.Groups(1)
      CType(g1.GroupFooter.DataModel, FarPoint.Win.Spread.Model.IAggregationSupport).SetCellAggregationType(0, 0, FarPoint.Win.Spread.Model.AggregationType.Sum)
      FpSpread1.ActiveSheet.Models.Data = gdm
  End Sub