Public Event ValueChanged(sender As Object, e As EventArgs)
    Public Sub New()
        Me.fNumericUpDown = New NumericUpDown() With {
            ...
        }
        AddHandler Me.fNumericUpDown.ValueChanged, AddressOf fNumericUpDown_ValueChanged
        ...
    End Sub
    Private Sub fNumericUpDown_ValueChanged(sender As Object, e As EventArgs)
      RaiseEvent ValueChanged(Me, e)
    End Sub
    Public ReadOnly Property Value() As Decimal
      Get
        Return Me.fNumericUpDown.Value
      End Get
    End Property

With MyGrid.Rows.Add
   ...
   Dim custEdit As igNumericUpDownCellEditor = New igNumericUpDownCellEditor
   .Cells(iCol).Style.CustomEditor = custEdit
   .Cells(iCol).Style.TextAlign = iGContentAlignment.MiddleCenter
   AddHandler custEdit.ValueChanged, AddressOf NumericUpDownCustomCellEditor_ValueChanged
   ...
End With

  Private Sub MyGridNumericUpDownCustomCellEditor_ValueChanged(sender As Object, e As EventArgs)
    For i As Integer = 0 To MyGrid.Rows.Count - 1
      For j As Integer = 0 To MyGrid.Cols.Count - 1
        If sender Is MyGrid.Rows(i).Cells(j).Style.CustomEditor Then
          If CDec(MyGrid.Rows(i).Cells(j).Value) <> CDec(CType(sender, igNumericUpDownCellEditor).Value) Then
            MyGrid.Rows(i).Cells(j).Value = CType(sender, igNumericUpDownCellEditor).Value
            DoOtherStuff
          End If
          Exit Sub
        End If
      Next
    Next
  End Sub