public RadForm1()
        {
            InitializeComponent();

            DataTable dt = new DataTable();
            dt.Columns.Add("Id", typeof(int));
            dt.Columns.Add("Title", typeof(string));
            dt.Columns.Add("Price", typeof(decimal));

            for (int i = 0; i < 10; i++)
            {
                dt.Rows.Add(i, "Row" + i, 0);
            }

            this.radGridView1.DataSource = dt;
            this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

            CustomSummaryItem summaryItem = new CustomSummaryItem("Price", "{0}",GridAggregateFunction.StDev);
           
            GridViewSummaryRowItem summaryRowItem = new GridViewSummaryRowItem();
            summaryRowItem.Add(summaryItem); 
            this.radGridView1.SummaryRowsBottom.Add(summaryRowItem);
        }

        public class CustomSummaryItem : GridViewSummaryItem
        {
            public CustomSummaryItem(string name, string formatString, GridAggregateFunction aggregate) : base(name, formatString, aggregate)
            {
            }

            [Description("Returns the standard deviation from the specified expression")]
            public override object Evaluate(IHierarchicalRow row)
            {
                decimal value = 0;
                try
                {
                    value = (decimal)base.Evaluate(row);
                }
                catch (Exception)
                {
                    return 0;
                }
                return value;
            }
        }