public void GetParkedPerMonth() { this.chart1.Series.Clear(); chart1.Series.Add("month"); // Set title chart1.Titles.Clear(); this.chart1.Titles.Add("Parked per Month"); // Add series. ManagerDAO dao = new ManagerDAO(); Hashtable Htable = dao.GetDataParked(cbUser.SelectedValue.ToString()); ICollection table = Htable.Keys; foreach (var item in table) { chart1.Series["month"].Points.AddXY(item, Htable[item]); } }