private void updateDisplay()
 {
     lblTotalCashflowAmount.Text = string.Format("{1:C}", ClsVehicleBusiness.VehicleList.Count, ClsVehicleBusiness.TotalCashflow());
     lstLicencePlates.DataSource = null;
     lstLicencePlates.DataSource = ClsVehicleBusiness.VehicleList.Values.ToList <ClsVehicle>();
 }